Merge pull request 'docs: rebrand the README as TheCloud's AWS runtime' (#11 ) from docs/readme-thecloud into main

Reviewed-on: #11
docs: rebrand the README as TheCloud's AWS runtime
2026-10-25 14:29:43 +00:00 · 2026-10-25 10:11:34 -04:00 · 2026-10-25 13:49:41 +00:00 · 2026-10-25 08:57:05 -04:00 · 2026-10-25 12:27:48 +00:00 · 2026-10-25 08:26:34 -04:00
52 changed files with 4469 additions and 537 deletions
@@ -1,21 +1,17 @@
 <p align="center">
-  <img src="docs/assets/floci-black.svg#gh-light-mode-only" alt="Floci" width="500" />
-  <img src="docs/assets/floci-white.svg#gh-dark-mode-only" alt="Floci" width="500" />
+  <img src="docs/assets/thecloud-logo.png" alt="TheCloud" width="160" />
 </p>

+<h1 align="center">TheCloud AWS runtime</h1>
+
 <p align="center">
  <strong>Any Cloud. Locally.</strong><br />
-  Light, fluffy, and always free<br />
+  The local AWS emulator behind TheCloud.<br />
  No account. No auth token. No feature gates. Just <code>docker compose up</code>.
 </p>

 <p align="center">
-  <a href="https://github.com/floci-io/floci/releases/latest"><img src="https://img.shields.io/github/v/release/floci-io/floci?label=latest%20release&color=blue" alt="Latest Release"></a>
-  <a href="https://github.com/floci-io/floci/actions/workflows/release.yml"><img src="https://img.shields.io/github/actions/workflow/status/floci-io/floci/release.yml?label=build" alt="Build Status"></a>
-  <a href="https://hub.docker.com/r/floci/floci"><img src="https://img.shields.io/docker/pulls/floci/floci?label=docker%20pulls" alt="Docker Pulls"></a>
-  <a href="https://hub.docker.com/r/floci/floci"><img src="https://img.shields.io/docker/image-size/floci/floci/latest?label=image%20size" alt="Docker Image Size"></a>
  <a href="https://opensource.org/licenses/MIT"><img src="https://img.shields.io/badge/license-MIT-green" alt="License: MIT"></a>
-  <a href="https://github.com/floci-io/floci/stargazers"><img src="https://img.shields.io/github/stars/floci-io/floci?style=flat" alt="GitHub Stars"></a>
 </p>

 <p align="center">
@@ -24,41 +20,43 @@
  <a href="#supported-services">Services</a> ·
  <a href="#sdk-integration">SDKs</a> ·
  <a href="#testcontainers">Testcontainers</a> ·
-  <a href="#migrating-from-localstack">Migration</a> ·
-  <a href="https://floci.io/floci/">Docs</a>
+  <a href="#migrating-from-localstack">Migration</a>
 </p>

 ---

-## What is Floci?
+## What is this?

-Floci is a free, open-source local AWS emulator for development, testing, and CI.
+TheCloud's AWS runtime is a local AWS emulator for development, testing, and CI. It is the runtime behind [TheCloud](https://gitea.zacksolutions.dev/Zakaria/floci-ui), a self-hosted cloud console.

-It gives you AWS-shaped services on your machine without requiring a cloud account, an auth token, or paid feature gates. Point your AWS SDK, CLI, Terraform, CDK, OpenTofu, or test suite at `http://localhost:4566` and keep your existing workflows.
+It gives you AWS-shaped services on your machine without a cloud account, an auth token, or paid feature gates. Point your AWS SDK, CLI, Terraform, CDK, OpenTofu, or test suite at `http://localhost:4566` and keep your existing workflows.

-Already using LocalStack? Floci is a drop-in replacement: swap the image and keep going. See [Migrating from LocalStack](#migrating-from-localstack).
+It is a fork of the open-source [Floci](https://github.com/floci-io/floci) emulator. Upstream fixes are brought in by cherry-picking from Floci's `main`, alongside TheCloud's own changes, for example:

-Floci is the AWS member of the [Floci](https://github.com/floci-io) emulator family, named after [floccus](https://en.wikipedia.org/wiki/Cirrocumulus_floccus), the cloud formation that looks like popcorn.
+- Cognito hosted login with identity-provider buttons, and `PreventUserExistenceErrors` honoured on app clients.
+- CloudFront distributions served at `<id>.cloudfront.localhost`.
+- SES delivering real email through an SMTP relay that signs in with a password (Gmail app passwords work).
+- HTTP API JWT authorizers that verify tokens from this runtime's own Cognito pools.

-| Emulator | Cloud | Port |
-|---|---|:---:|
-| **[floci](https://github.com/floci-io/floci)** | **AWS** | **4566** |
-| [floci-az](https://github.com/floci-io/floci-az) | Azure | 4577 |
-| [floci-gcp](https://github.com/floci-io/floci-gcp) | GCP | 4588 |
-| [floci-oci](https://github.com/floci-io/floci-oci) | OCI | 4599 |
+Companion runtimes for other clouds come from upstream: [floci-az](https://github.com/floci-io/floci-az) for Azure on port 4577 and [floci-gcp](https://github.com/floci-io/floci-gcp) for GCP on port 4588.

 ## Quick Start

-The fastest way to run Floci is with the official [CLI](https://github.com/floci-io/floci-cli)
+Build and start the runtime from this repository:

 ```bash
-floci start
+git clone https://gitea.zacksolutions.dev/Zakaria/FlociClone.git
+cd FlociClone
+docker compose up -d
 ```

 Export the AWS environment variables:

 ```bash
-eval $(floci env)
+export AWS_ENDPOINT_URL=http://localhost:4566
+export AWS_DEFAULT_REGION=us-east-1
+export AWS_ACCESS_KEY_ID=test
+export AWS_SECRET_ACCESS_KEY=test
 ```

 Use your existing AWS tools normally:
@@ -75,121 +73,41 @@ aws dynamodb create-table \
 aws dynamodb list-tables
 ```

-### Watch it run
-
-This short demo shows the CLI flow: start Floci, export the local AWS environment, run standard AWS CLI commands, and stop the emulator.
-
-https://github.com/user-attachments/assets/b55714dc-ef36-40ae-a734-cd2cadc288a8
-
 All AWS services are available at `http://localhost:4566`. Any region works. Credentials can be any non-empty values unless you explicitly enable stricter service-specific auth checks.

 <details>
-<summary>Prefer Docker Compose?</summary>
+<summary>Prefer <code>docker run</code>, or dev mode?</summary>

-Create a `compose.yaml` file:
-
-```yaml
-services:
-  floci:
-    image: floci/floci:latest
-    ports:
-      - "4566:4566"
-```
-
-Start Floci:
+Build the image, then run it with the Docker socket so container-backed services work:

 ```bash
-docker compose up
+docker build -f docker/Dockerfile -t floci-floci:latest .
+docker run -d --name floci -p 4566:4566 \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  floci-floci:latest
 ```

-Then configure your AWS environment manually:
+Or run it in Quarkus dev mode, which needs JDK 25:

 ```bash
-export AWS_ENDPOINT_URL=http://localhost:4566
-export AWS_DEFAULT_REGION=us-east-1
-export AWS_ACCESS_KEY_ID=test
-export AWS_SECRET_ACCESS_KEY=test
+./mvnw quarkus:dev
 ```

 </details>

-<details>
-<summary>Using the old <code>hectorvent/floci</code> image?</summary>
-
-Update your image name:
-
-```yaml
-# Before
-image: hectorvent/floci:latest
-
-# After
-image: floci/floci:latest
-```
-
-The old `hectorvent/floci` repository no longer receives updates.
-
-</details>
-
 ## Web Console

-Floci ships a browser console for inspecting the resources in your local emulator.
+[TheCloud](https://gitea.zacksolutions.dev/Zakaria/floci-ui) is the console for this runtime. It runs as its own app on port 4500, talks to the runtime at `FLOCI_ENDPOINT`, and covers the services listed in its README.

-**Open it at:** `http://localhost:4566/_floci/ui`
-
-Nothing runs at boot. The first request pulls the console image, starts it as a sidecar container on Floci's Docker network, hands it Floci's own reachable address plus the standard AWS environment, polls its health endpoint, and redirects the browser once it reports it can reach Floci. The sidecar's port is bound by Docker, so it needs no `ports:` entry of your own, and its logs are streamed into CloudWatch Logs under `/floci/ui`.
-
-Starting a container needs the Docker socket:
-
-```yaml
-services:
-  floci:
-    image: floci/floci:latest
-    ports:
-      - "4566:4566"
-    volumes:
-      - /var/run/docker.sock:/var/run/docker.sock
-```
+The runtime can also start a console for you as a sidecar container on first visit to `http://localhost:4566/_floci/ui`. That needs the Docker socket, and the image is set with `FLOCI_SERVICES_UI_IMAGE`; point it at your TheCloud build to use it.

 | Variable | Default | Description |
 |---|---|---|
 | `FLOCI_SERVICES_UI_ENABLED` | `true` | Enable the console sidecar |
-| `FLOCI_SERVICES_UI_IMAGE` | `floci/floci-ui:latest` | Console image to run |
+| `FLOCI_SERVICES_UI_IMAGE` | `floci/floci-ui:latest` | Console image to run, for example `floci/floci-ui:local` for a local TheCloud build |
 | `FLOCI_SERVICES_UI_CONTAINER_NAME` | `floci-ui` | Name of the sidecar container |
 | `FLOCI_SERVICES_UI_PORT` | `4500` | Host port the console is published on |
-| `FLOCI_SERVICES_UI_KEEP_RUNNING_ON_SHUTDOWN` | `false` | Leave the sidecar running when Floci stops |
-
-### Running a different console
-
-The console is not fixed to the one Floci ships. Any console implementing the [Floci console contract](https://floci.io/floci/ui/console-contract/) runs with nothing but an image name: listen on the port in `PORT`, serve `GET /api/health`, talk to Floci at `AWS_ENDPOINT_URL`.
-
-```yaml
-environment:
-  FLOCI_SERVICES_UI_IMAGE: acme/my-console:1.0
-```
-
-A console that differs from the contract's defaults says so in its own `io.floci.console.*` image labels, so its operators do not have to. [StackPort](https://github.com/DaviReisVieira/stackport), for example, listens on 8080 rather than 4500; on an image that predates the labels, say it by hand:
-
-```yaml
-environment:
-  FLOCI_SERVICES_UI_IMAGE: davireis/stackport:latest
-  FLOCI_SERVICES_UI_CONTAINER_NAME: floci-stackport
-  FLOCI_SERVICES_UI_PORT: "8080"
-  FLOCI_SERVICES_UI_INTERNAL_PORT: "8080"
-```
-
-[Floci Dash](https://github.com/ofsazib/floci-dash) is another. It honours `PORT`, so only the two things it does differ on need naming:
-
-```yaml
-environment:
-  FLOCI_SERVICES_UI_IMAGE: ghcr.io/ofsazib/floci-dash:latest
-  FLOCI_SERVICES_UI_CONTAINER_NAME: floci-dash
-  FLOCI_SERVICES_UI_ENDPOINT_ENV: FLOCI_URL
-  FLOCI_SERVICES_UI_STATUS_PATH: /api/healthz
-```
-
-The endpoint itself is never configured by hand: Floci resolves its own reachable address at start time and injects it as `AWS_ENDPOINT_URL`.
-
-Full reference: [Web Console](https://floci.io/floci/ui/) and [Console Contract v1](https://floci.io/floci/ui/console-contract/).
+| `FLOCI_SERVICES_UI_KEEP_RUNNING_ON_SHUTDOWN` | `false` | Leave the sidecar running when the runtime stops |

 ## Features

@@ -212,14 +130,7 @@ Lambda, RDS, Neptune, ElastiCache, MSK, MSK Connect, ECS, EC2, EKS, OpenSearch,

 Point standard AWS clients at `http://localhost:4566`. Existing credentials, regions, SDKs, CLI commands, and IaC workflows stay familiar.

-Terraform can provision AWS-shaped resources locally through Floci using the standard HashiCorp AWS provider. See the [Terraform with Floci guide](docs/getting-started/terraform.md) for provider configuration, resource examples, and optional emulated S3 state.
-
-</details>
-
-<details>
-<summary><strong>Fast enough for CI</strong></summary>
-
-The native image starts in milliseconds and keeps idle memory low, making it practical for local development and test pipelines.
+Terraform can provision AWS-shaped resources locally through this runtime using the standard HashiCorp AWS provider. See the [Terraform guide](docs/getting-started/terraform.md) for provider configuration, resource examples, and optional emulated S3 state.

 </details>

@@ -230,36 +141,13 @@ Choose from in-memory, persistent, hybrid, and write-ahead log storage depending

 </details>

-## Why Floci?
-
-LocalStack's community edition [sunset in March 2026](https://blog.localstack.cloud/the-road-ahead-for-localstack/), requiring auth tokens and freezing security updates. Floci is the no-strings-attached alternative.
-
-| Capability | Floci | LocalStack Community |
-|---|:---:|:---:|
-| Auth token required | No | Yes |
-| Security updates | Yes | Frozen |
-| Startup time | ~24 ms | ~3.3 s |
-| Idle memory | ~13 MiB | ~143 MiB |
-| Docker image size | ~90 MB | ~1.0 GB |
-| License | MIT | Restricted |
-| API Gateway v2 / HTTP API | Yes | No |
-| Cognito | Yes | No |
-| RDS, ElastiCache, MSK, MSK Connect | Real Docker | No |
-| Neptune (graph DB + Gremlin WebSocket) | Real Docker | No |
-| DocumentDB (MongoDB-compatible) | Real Docker | No |
-| ECS, EC2, EKS | Real Docker | No |
-| CodeBuild | Real Docker execution | No |
-| Native binary | ~40 MB | No |
-
-**Broad AWS coverage. Free forever.** See the [Services Overview](https://floci.io/floci/services/) for the full list of emulated services.
-
 ## Architecture Overview

 ```mermaid
 flowchart LR
    Client["AWS SDK / CLI"]

-    subgraph Floci ["Floci, port 4566"]
+    subgraph Runtime ["TheCloud AWS runtime, port 4566"]
        Router["HTTP Router\nJAX-RS / Vert.x"]

        subgraph Stateless ["Stateless Services"]
@@ -288,7 +176,7 @@ flowchart LR

 ## Supported Services

-Floci supports local emulation for application services, data services, eventing, identity, infrastructure, billing, and container-backed workloads.
+The runtime emulates application services, data services, eventing, identity, infrastructure, billing, and container-backed workloads.

 | Category | Services |
 |---|---|
@@ -303,7 +191,7 @@ Floci supports local emulation for application services, data services, eventing
 | Cost and billing | AWS Budgets, Pricing, Cost Explorer, Cost and Usage Reports, BCM Pricing Calculator, BCM Data Exports |
 | Resilience, backup, and config | AWS FIS, AWS Backup, AWS Config, AppConfig, AppConfigData, CloudFormation, Cloud Control API |

-For operation-level compatibility, see the [Services Overview](https://floci.io/floci/services/).
+For operation-level detail, see upstream Floci's [Services Overview](https://floci.io/floci/services/); it can list upstream work this fork has not picked up yet.

 <details>
 <summary>Detailed service notes</summary>
@@ -378,7 +266,7 @@ For operation-level compatibility, see the [Services Overview](https://floci.io/
 | AWS Backup | In-process | Vaults, backup plans, selections, simulated job lifecycle, recovery points |
 | AWS FIS | In-process | All 26 management APIs for templates, experiments, target accounts, action and target discovery, safety lever, tagging, and pagination; experiment execution is a safe control-plane simulation and does not inject faults into other services |
 | AWS Config | In-process | Config rules, evaluation-driven compliance (PutEvaluations, compliance details and summaries), configuration recorders, delivery channels, retention configuration, conformance packs, tagging |
-| Organizations | In-process | Organizations, roots, nested OUs, member accounts, all policy types with `FullAWSAccess` and effective-policy inheritance, trusted service access, delegated administrators, resource policy, and the full invitation/handshake flow; created accounts are usable Floci accounts and member accounts can read the organization they belong to |
+| Organizations | In-process | Organizations, roots, nested OUs, member accounts, all policy types with `FullAWSAccess` and effective-policy inheritance, trusted service access, delegated administrators, resource policy, and the full invitation/handshake flow; created accounts are usable accounts in the runtime and member accounts can read the organization they belong to |
 | CloudTrail | In-process | Trails, event selectors (S3 data events with bucket/prefix matching), `StartLogging`/`StopLogging`, scheduled gzipped log file emission to the destination bucket at AWS-shaped key paths, IAM-deny path emits `AccessDenied` records |
 | CloudFront | In-process | Distributions, origins, cache behaviors, invalidations, tagging |
 | WAF v2 | In-process | Web ACLs, IP sets, regex pattern sets, rule groups, logging configs, resource associations, tagging (REGIONAL and CLOUDFRONT scopes) |
@@ -389,7 +277,7 @@ For operation-level compatibility, see the [Services Overview](https://floci.io/
 | Textract | In-process stub | API-compatible stubs, dummy block data, async job simulation |
 | Transcribe | In-process stub | Transcription jobs and custom vocabularies; jobs complete immediately, no real audio processing |
 | Pricing | In-process with static snapshot | Product discovery, attributes, price list files, pagination |
-| Cost Explorer | In-process | Cost synthesized from Floci resource state and pricing snapshots |
+| Cost Explorer | In-process | Cost synthesized from the runtime's resource state and pricing snapshots |
 | Cost and Usage Reports | In-process with floci-duck sidecar | CUR 2.0 and FOCUS 1.2 columns, account-scoped storage, Parquet emission |
 | BCM Pricing Calculator | In-process | Workload estimate create, usage pricing, read, and delete lifecycle |
 | BCM Data Exports | In-process | Export lifecycle, executions, update and delete operations |
@@ -398,7 +286,7 @@ For operation-level compatibility, see the [Services Overview](https://floci.io/

 ## Real Docker Integration

-Floci uses real Docker containers when in-process emulation would reduce fidelity. This applies to stateful databases, connection-heavy protocols, runtimes, and build systems.
+The runtime uses real Docker containers when in-process emulation would reduce fidelity. This applies to stateful databases, connection-heavy protocols, runtimes, and build systems.

 | Service | Default image | What is real |
 |---|---|---|
@@ -416,12 +304,12 @@ Floci uses real Docker containers when in-process emulation would reduce fidelit
 | EC2 | AMI-mapped Linux images | Linux containers, SSH key injection, UserData, IMDS, IAM credentials |
 | ECS | User-specified task image | Container lifecycle, start, stop, health checks |
 | EKS | `rancher/k3s:latest` | Kubernetes API server via k3s |
-| MWAA | `apache/airflow:<version>-python3.12` + `postgres:16-alpine` | Real Apache Airflow (LocalExecutor: scheduler + webserver) with its own Postgres metadata DB; webserver/CLI reachable via Floci's proxy |
+| MWAA | `apache/airflow:<version>-python3.12` + `postgres:16-alpine` | Real Apache Airflow (LocalExecutor: scheduler + webserver) with its own Postgres metadata DB; webserver/CLI reachable via the runtime's proxy |
 | CodeBuild | User-specified environment image | Buildspec execution, log streaming, S3 artifact upload |
 | OpenSearch | `opensearchproject/opensearch:2` | Full OpenSearch engine with REST API |
 | ECR | `registry:2` | OCI-compatible registry for docker push and docker pull |
-| Verified Permissions | `floci/floci-sidecar-cedar:1.1.0` | Cedar 4 policy parsing, schema validation and authorization decisions, via a [Floci sidecar](https://github.com/floci-io/floci-sidecars) |
-| AppSync | `floci/floci-sidecar-graphql:0.2.0` | graphql-java schema validation, query planning and execution, via a [Floci sidecar](https://github.com/floci-io/floci-sidecars) |
+| Verified Permissions | `floci/floci-sidecar-cedar:1.1.0` | Cedar 4 policy parsing, schema validation and authorization decisions, via an upstream [Floci sidecar](https://github.com/floci-io/floci-sidecars) |
+| AppSync | `floci/floci-sidecar-graphql:0.2.0` | graphql-java schema validation, query planning and execution, via an upstream [Floci sidecar](https://github.com/floci-io/floci-sidecars) |

 Docker-backed services require the Docker socket:

@@ -430,7 +318,7 @@ docker run -d --name floci \
  -p 4566:4566 \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -u root \
-  floci/floci:latest
+  floci-floci:latest
 ```

 ### Overriding default images
@@ -454,7 +342,7 @@ docker run -d --name floci \

 ## Persistence and Storage Modes

-Floci can trade speed for durability depending on the workflow. Configure the default mode with `FLOCI_STORAGE_MODE`, or override storage per service.
+The runtime can trade speed for durability depending on the workflow. Configure the default mode with `FLOCI_STORAGE_MODE`, or override storage per service.

 | Mode | Behavior | Best for | Durability |
 |---|---|---|:---:|
@@ -465,22 +353,22 @@ Floci can trade speed for durability depending on the workflow. Configure the de

 Use `memory` for fast test runs. Use `hybrid` when you want state preserved across container restarts without much overhead.

-For more detail, see the [Storage Configuration documentation](https://floci.io/floci/configuration/storage/).
+For more detail, see upstream Floci's [Storage Configuration documentation](https://floci.io/floci/configuration/storage/).

 ## Multi-Account Isolation

-Floci supports per-account resource isolation with no extra setup. If `AWS_ACCESS_KEY_ID` is exactly 12 digits, Floci uses it as the account ID. Resources created by one account are invisible to another.
+The runtime supports per-account resource isolation with no extra setup. If `AWS_ACCESS_KEY_ID` is exactly 12 digits, it is used as the account ID. Resources created by one account are invisible to another.

 ```bash
 AWS_ACCESS_KEY_ID=111111111111 aws sqs create-queue --queue-name orders
 AWS_ACCESS_KEY_ID=222222222222 aws sqs create-queue --queue-name orders
 ```

-Any other key format, such as `test` or `AKIA...`, causes Floci to fall back to `FLOCI_DEFAULT_ACCOUNT_ID`, which defaults to `000000000000`.
+Any other key format, such as `test` or `AKIA...`, falls back to `FLOCI_DEFAULT_ACCOUNT_ID`, which defaults to `000000000000`.

 STS temporary credentials are routed too: credentials from `AssumeRole` resolve to the assumed role's account, so the cross-account assume-role-then-provision pattern works locally. Resolution precedence is 12-digit AKID → temporary-session lookup → `FLOCI_DEFAULT_ACCOUNT_ID`.

-See the [Multi-Account Isolation docs](https://floci.io/floci/configuration/multi-account/).
+See upstream Floci's [Multi-Account Isolation docs](https://floci.io/floci/configuration/multi-account/).

 ## SDK Integration

@@ -526,7 +414,7 @@ client = boto3.client(

 client.put_parameter(
    Name="/demo/app/message",
-    Value="hello from floci",
+    Value="hello from TheCloud",
    Type="String",
    Overwrite=True,
 )
@@ -552,7 +440,7 @@ const client = new SQSClient({
 await client.send(
  new SendMessageCommand({
    QueueUrl: "http://localhost:4566/000000000000/demo-queue",
-    MessageBody: "hello from floci",
+    MessageBody: "hello from TheCloud",
  }),
 );
 ```
@@ -613,7 +501,7 @@ use aws_sdk_secretsmanager::Client;
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = aws_config::defaults(aws_config::BehaviorVersion::latest())
        .region(Region::new("us-east-1"))
-        .credentials_provider(Credentials::new("test", "test", None, None, "floci"))
+        .credentials_provider(Credentials::new("test", "test", None, None, "thecloud"))
        .endpoint_url("http://localhost:4566")
        .load()
        .await;
@@ -623,7 +511,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
    client
        .create_secret()
        .name("demo/secret")
-        .secret_string("hello from floci")
+        .secret_string("hello from TheCloud")
        .send()
        .await?;

@@ -649,7 +537,7 @@ aws --endpoint-url http://localhost:4566 s3 ls

 ## Testcontainers

-Floci has Testcontainers modules for starting isolated Floci instances directly from tests. This avoids shared state, manual daemon setup, and port conflicts.
+Upstream Floci publishes Testcontainers modules for starting isolated instances directly from tests. This avoids shared state, manual daemon setup, and port conflicts. They start upstream's `floci/floci` image by default, so they test against upstream Floci rather than this fork unless you give them your own image.

 For Testcontainers 1.x, use the versions as indicated in the table below.

@@ -767,7 +655,7 @@ def test_s3_create_bucket():

 ## Compatibility Testing

-The [`compatibility-tests`](./compatibility-tests/) directory validates Floci across SDKs and tooling workflows.
+The [`compatibility-tests`](./compatibility-tests/) directory validates the runtime across SDKs and tooling workflows.

 | Module | Language / Tool | SDK / Client | Tests |
 |---|---|---|---:|
@@ -784,22 +672,19 @@ The [`compatibility-tests`](./compatibility-tests/) directory validates Floci ac

 ## Migrating from LocalStack

-Floci is a drop-in replacement for LocalStack Community. The port, credentials, SDK configuration, and CLI endpoint pattern work the same way. Swap the image and keep going.
+The runtime is a drop-in replacement for LocalStack Community. The port, credentials, SDK configuration, and CLI endpoint pattern work the same way. Swap the image and keep going.

 ```yaml
 # Before
 image: localstack/localstack

-# After, standard image
-image: floci/floci:latest
-
-# After, if init scripts need AWS CLI or boto3
-image: floci/floci:latest-compat
+# After, your local build of this repository
+image: floci-floci:latest
 ```

 LocalStack environment variables are translated automatically:

-| LocalStack | Floci equivalent |
+| LocalStack | Equivalent |
 |---|---|
 | `LOCALSTACK_HOST` | `FLOCI_HOSTNAME` |
 | `PERSISTENCE=1` | `FLOCI_STORAGE_MODE=persistent` |
@@ -809,43 +694,23 @@ LocalStack environment variables are translated automatically:

 Init scripts mounted under `/etc/localstack/init/` run unchanged. The `/_localstack/init` and `/_localstack/health` endpoints are still served. Once the emulator is up, the log also ends with a LocalStack-style `Ready.` line, so tooling that watches the log for it, such as the default wait strategy of Testcontainers' `LocalStackContainer`, works unchanged. Set `LOCALSTACK_PARITY=false` to opt out of automatic translation.

-See the [full migration guide](https://floci.io/floci/getting-started/migrate-from-localstack/).
+See upstream Floci's [full migration guide](https://floci.io/floci/getting-started/migrate-from-localstack/).

-## Image Tags
+## Building and Updating

-Every tag combines a variant and a channel.
+The image is built from this repository; nothing is published to Docker Hub:

-| Channel | Standard | Baseline (ARM64 only) | Compat with AWS CLI and boto3 |
-|---|---|---|---|
-| Release, floating | `latest` | `latest-baseline` | `latest-compat` |
-| Release, pinned | `x.y.z` | `x.y.z-baseline` | `x.y.z-compat` |
-| Nightly, floating | `nightly` | — | `nightly-compat` |
-| Nightly, dated | `nightly-mmddyyyy` | — | `nightly-mmddyyyy-compat` |
-
-Use `latest` for stable releases, a pinned version for reproducible builds, and `nightly` to track `main`.
-
-```yaml
-# Recommended
-image: floci/floci:latest
-
-# Includes AWS CLI and boto3
-image: floci/floci:latest-compat
-
-# ARM64 baseline for Raspberry Pi 4 / pre-LSE cores
-image: floci/floci:latest-baseline
-
-# Pinned release
-image: floci/floci:x.y.z
-
-# Track main
-image: floci/floci:nightly
+```bash
+docker build -f docker/Dockerfile -t floci-floci:latest .
 ```

-### Release train
+Tests run with Maven and JDK 25:

-Stable releases ship on the **1st and 3rd Tuesday of each month**. Between trains, `floci/floci:nightly` tracks `main`. Every merged fix is available the next day, and dated `nightly-mmddyyyy` tags let you pin a specific night's build.
+```bash
+./mvnw test
+```

-Versions are derived from Conventional Commits by [semantic-release](https://github.com/semantic-release/semantic-release); `CHANGELOG.md` is generated, never hand-edited. Releases are cut from `main` only: there are no maintenance branches.
+Upstream fixes come in by cherry-picking commits from Floci's `main` onto a branch, which then goes through review like any other change.

 ## Configuration

@@ -853,26 +718,26 @@ All settings are overridable through environment variables with the `FLOCI_` pre

 | Variable | Default | Description |
 |---|---|---|
-| `FLOCI_PORT` | `4566` | Port exposed by the Floci API |
+| `FLOCI_PORT` | `4566` | Port the runtime's API listens on |
 | `FLOCI_DEFAULT_REGION` | `us-east-1` | Default AWS region |
 | `FLOCI_DEFAULT_ACCOUNT_ID` | `000000000000` | Default AWS account ID |
-| `FLOCI_BASE_URL` | `http://localhost:4566` | Base URL used when Floci returns service URLs |
-| `FLOCI_HOSTNAME` | Unset | Hostname used in returned URLs when Floci runs inside Docker Compose |
+| `FLOCI_BASE_URL` | `http://localhost:4566` | Base URL used in service URLs the runtime returns |
+| `FLOCI_HOSTNAME` | Unset | Hostname used in returned URLs when the runtime runs inside Docker Compose |
 | `FLOCI_STORAGE_MODE` | `memory` | Storage mode: `memory`, `persistent`, `hybrid`, or `wal` |
 | `FLOCI_STORAGE_PERSISTENT_PATH` | `./data` | Directory used for persisted state |
 | `FLOCI_SERVICES_LAMBDA_ECR_BASE_URI` | `public.ecr.aws` | ECR base URI used when pulling Lambda runtime images (legacy name `FLOCI_ECR_BASE_URI` still works) |
 | `FLOCI_SERVICES_S3_ENFORCE_AUTH` | `false` | Enforce S3 public/private read access and reject unknown signed S3 access keys |

-Full reference: [configuration docs](https://floci.io/floci/configuration/advanced/application-yml)
+Full reference: [`src/main/resources/application.yml`](src/main/resources/application.yml), and upstream Floci's [configuration docs](https://floci.io/floci/configuration/advanced/application-yml).

 ### Multi-container Docker Compose

-When your application runs in a different container, set `FLOCI_HOSTNAME` to the Floci service name so returned URLs, such as SQS `QueueUrl` values, resolve correctly.
+When your application runs in a different container, set `FLOCI_HOSTNAME` to the runtime's service name so returned URLs, such as SQS `QueueUrl` values, resolve correctly.

 ```yaml
 services:
  floci:
-    image: floci/floci:latest
+    image: floci-floci:latest
    ports:
      - "4566:4566"
    environment:
@@ -887,59 +752,6 @@ services:

 Without this, services may return URLs using `localhost`, which points to the wrong container from the application container.

-## Community
-
-Join the Floci community on [Slack](https://join.slack.com/t/floci/shared_invite/zt-3tjn02s3q-A00kEjJ1cZxsg_imTfy6Cw) or [GitHub Discussions](https://github.com/orgs/floci-io/discussions). Feature ideas, compatibility questions, design tradeoffs, and rough proposals are welcome.
-
-## Sponsors
-
-Floci is independent open source, funded by the people and companies who use it.
-Sponsorship buys gratitude and nothing else: every emulated service is free for
-everyone, forever, and no sponsor gets features, priority, or roadmap influence
-that the rest of the Flock does not.
-
-### 🥇 Gold
-
-Large logo with top placement in the emulator READMEs and on floci.io, plus a
-mention in release notes.
-
-[IceGuard](https://github.com/iceguard) · [Softmax](https://softmax.com/)
-
-### 🥈 Silver
-
-Logo in the emulator READMEs and on floci.io, plus a mention in release notes.
-
-*Your logo here. [Become a sponsor](https://github.com/sponsors/floci-io).*
-
-### 🥉 Community
-
-Name in the emulator READMEs, a sponsor badge on GitHub, and our sincere thanks.
-
-[AutoScout24](https://www.autoscout24.com) · [Nexxion AI](https://nexxion.ai/)
-
-Every sponsor, including the Friends of the Flock who support Floci outside these
-tiers, is listed in [THANKS.md](https://github.com/floci-io/.github/blob/main/THANKS.md).
-
-**[Sponsor Floci](https://github.com/sponsors/floci-io)**
-
-## Star History
-
-<p align="center">
-  <a href="https://www.star-history.com/?repos=floci-io%2Ffloci&type=date&legend=top-left">
-    <picture>
-      <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/chart?repos=floci-io/floci&type=date&theme=dark&legend=top-left" />
-      <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/chart?repos=floci-io/floci&type=date&legend=top-left" />
-      <img width="600" alt="Star History Chart" src="https://api.star-history.com/chart?repos=floci-io/floci&type=date&legend=top-left" />
-    </picture>
-  </a>
-</p>
-
-## Contributors
-
-<a href="https://github.com/floci-io/floci/graphs/contributors">
-  <img src="https://contrib.rocks/image?repo=floci-io/floci&max=100&columns=20" />
-</a>
-
 ## License

-MIT. Use it however you want.
+MIT. TheCloud's AWS runtime is a fork of [Floci](https://github.com/floci-io/floci); thanks to the Floci contributors and sponsors whose work it builds on.
@@ -0,0 +1,117 @@
+package com.floci.test;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import software.amazon.awssdk.services.cloudwatch.CloudWatchClient;
+import software.amazon.awssdk.services.cloudwatch.model.ComparisonOperator;
+import software.amazon.awssdk.services.cloudwatch.model.Dimension;
+import software.amazon.awssdk.services.cloudwatch.model.Metric;
+import software.amazon.awssdk.services.cloudwatch.model.MetricAlarm;
+import software.amazon.awssdk.services.cloudwatch.model.MetricDataQuery;
+import software.amazon.awssdk.services.cloudwatch.model.MetricStat;
+import software.amazon.awssdk.services.cloudwatch.model.StandardUnit;
+import software.amazon.awssdk.services.cloudwatch.model.Statistic;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@DisplayName("CloudWatch - Metric-math alarm definitions")
+class CloudWatchMetricMathAlarmTest {
+
+    private CloudWatchClient cloudWatch;
+    private String alarmName;
+
+    @BeforeEach
+    void setup() {
+        cloudWatch = TestFixtures.cloudWatchClient();
+        alarmName = TestFixtures.uniqueName("sdk-metric-math-alarm");
+    }
+
+    @AfterEach
+    void cleanup() {
+        try {
+            cloudWatch.deleteAlarms(request -> request.alarmNames(alarmName));
+        } finally {
+            cloudWatch.close();
+        }
+    }
+
+    @Test
+    void metricsRoundTripWithoutInventingSingleMetricFields() {
+        List<MetricDataQuery> metrics = metrics();
+        putMathAlarm(metrics);
+        assertMathAlarm(metrics);
+    }
+
+    @Test
+    void updatesReplaceQueriesAndSwitchBackToASingleMetric() {
+        putSingleMetricAlarm(300);
+        List<MetricDataQuery> original = metrics();
+        putMathAlarm(original);
+        assertMathAlarm(original);
+
+        List<MetricDataQuery> replacement = List.of(
+                original.get(0).toBuilder().expression("errors / requests").label("Ratio").build(),
+                original.get(1), original.get(2));
+        putMathAlarm(replacement);
+        assertMathAlarm(replacement);
+
+        putSingleMetricAlarm(120);
+        MetricAlarm alarm = describe();
+        assertThat(alarm.hasMetrics()).isFalse();
+        assertThat(alarm.period()).isEqualTo(120);
+        assertThat(alarm.metricName()).isEqualTo("5xx");
+        assertThat(alarm.namespace()).isEqualTo("AWS/ApiGateway");
+    }
+
+    private void putMathAlarm(List<MetricDataQuery> metrics) {
+        cloudWatch.putMetricAlarm(request -> request.alarmName(alarmName)
+                .comparisonOperator(ComparisonOperator.GREATER_THAN_THRESHOLD)
+                .evaluationPeriods(2).threshold(5.0).metrics(metrics));
+    }
+
+    private void putSingleMetricAlarm(int period) {
+        cloudWatch.putMetricAlarm(request -> request.alarmName(alarmName)
+                .comparisonOperator(ComparisonOperator.GREATER_THAN_THRESHOLD)
+                .evaluationPeriods(2).threshold(5.0).namespace("AWS/ApiGateway")
+                .metricName("5xx").statistic(Statistic.SUM).period(period));
+    }
+
+    private MetricAlarm describe() {
+        List<MetricAlarm> alarms = cloudWatch.describeAlarms(request -> request.alarmNames(alarmName)).metricAlarms();
+        assertThat(alarms).hasSize(1);
+        return alarms.get(0);
+    }
+
+    private void assertMathAlarm(List<MetricDataQuery> metrics) {
+        MetricAlarm alarm = describe();
+        assertThat(alarm.metrics()).containsExactlyElementsOf(metrics);
+        assertThat(alarm.period()).isNull();
+        assertThat(alarm.metricName()).isNull();
+        assertThat(alarm.namespace()).isNull();
+        assertThat(alarm.statistic()).isNull();
+        assertThat(alarm.extendedStatistic()).isNull();
+        assertThat(alarm.unit()).isNull();
+        assertThat(alarm.hasDimensions()).isFalse();
+        assertThat(alarm.evaluationPeriods()).isEqualTo(2);
+        assertThat(alarm.threshold()).isEqualTo(5.0);
+    }
+
+    private static List<MetricDataQuery> metrics() {
+        return List.of(
+                MetricDataQuery.builder().id("rate").expression("100 * errors / requests")
+                        .returnData(true).period(300).label("Error <rate> & requests").build(),
+                MetricDataQuery.builder().id("errors").returnData(false).accountId("123456789012")
+                        .metricStat(MetricStat.builder().period(300).stat("Sum").unit(StandardUnit.COUNT)
+                                .metric(Metric.builder().namespace("AWS/ApiGateway").metricName("5xx")
+                                        .dimensions(Dimension.builder().name("ApiName").value("api<&>").build())
+                                        .build()).build()).build(),
+                MetricDataQuery.builder().id("requests").returnData(false)
+                        .metricStat(MetricStat.builder().period(300).stat("Sum")
+                                .metric(Metric.builder().namespace("AWS/ApiGateway").metricName("Count").build())
+                                .build()).build());
+    }
+}
@@ -6,6 +6,7 @@ import software.amazon.awssdk.services.cloudwatch.model.*;

 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
+import java.util.Map;

 import static org.assertj.core.api.Assertions.*;

@@ -185,4 +186,67 @@ class CloudWatchTest {
        );
        assertThat(noMatch.datapoints()).isEmpty();
    }
+
+    @Test
+    @DisplayName("PutMetricData stores datums nested under EntityMetricData")
+    void testPutMetricDataWithEntityMetricData() {
+        String namespace = "JavaTestEntityMetricData";
+        Instant now = Instant.now();
+
+        cloudWatchClient.putMetricData(request -> request
+                .namespace(namespace)
+                .metricData(datum -> datum
+                        .metricName("TopLevel")
+                        .value(1.0)
+                        .timestamp(now))
+                .entityMetricData(entityMetricData -> entityMetricData
+                        .entity(entity -> entity
+                                .keyAttributes(Map.of(
+                                        "Type", "AWS::Resource",
+                                        "ResourceType", "AWS::EC2::Instance",
+                                        "Identifier", "i-0123456789abcdef0")))
+                        .metricData(MetricDatum.builder()
+                                .metricName("mem_used_percent")
+                                .value(6.5)
+                                .unit(StandardUnit.PERCENT)
+                                .storageResolution(60)
+                                .timestamp(now)
+                                .dimensions(Dimension.builder().name("host").value("h1").build())
+                                .build()))
+                .strictEntityValidation(false)
+        );
+
+        ListMetricsResponse listed = cloudWatchClient.listMetrics(request -> request.namespace(namespace));
+        assertThat(listed.metrics())
+                .extracting(Metric::metricName)
+                .containsExactlyInAnyOrder("TopLevel", "mem_used_percent");
+
+        GetMetricStatisticsResponse stats = cloudWatchClient.getMetricStatistics(request -> request
+                .namespace(namespace)
+                .metricName("mem_used_percent")
+                .dimensions(Dimension.builder().name("host").value("h1").build())
+                .startTime(now.minus(1, ChronoUnit.HOURS))
+                .endTime(now.plus(1, ChronoUnit.MINUTES))
+                .period(3600)
+                .statistics(Statistic.SUM)
+        );
+        assertThat(stats.datapoints()).hasSize(1);
+        assertThat(stats.datapoints().get(0).sum()).isEqualTo(6.5);
+    }
+
+    @Test
+    @DisplayName("PutMetricData without MetricName throws MissingRequiredParameterException")
+    void testPutMetricDataWithoutMetricNameIsRejected() {
+        String namespace = "JavaTestMissingMetricName";
+
+        assertThatThrownBy(() -> cloudWatchClient.putMetricData(request -> request
+                .namespace(namespace)
+                .entityMetricData(entityMetricData -> entityMetricData
+                        .metricData(MetricDatum.builder().value(1.0).build()))))
+                .isInstanceOf(MissingRequiredParameterException.class)
+                .satisfies(e -> assertThat(((MissingRequiredParameterException) e).awsErrorDetails().errorCode())
+                        .isEqualTo("MissingParameter"));
+
+        assertThat(cloudWatchClient.listMetrics(request -> request.namespace(namespace)).metrics()).isEmpty();
+    }
 }
@@ -203,6 +203,8 @@ class TestCloudWatchAlarms:

            alarm = next(a for a in alarms if a["AlarmName"] == alarm_name)
            assert alarm["StateValue"] == "INSUFFICIENT_DATA"
+            assert response["CompositeAlarms"] == []
+            assert response["LogAlarms"] == []
        finally:
            cloudwatch_client.delete_alarms(AlarmNames=[alarm_name])

@@ -12,6 +12,11 @@ services:
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - ./data:/app/data
+    # Optional SES SMTP relay settings (FLOCI_SERVICES_SES_SMTP_*), kept outside the repo
+    # because they hold a password. Without the file, sent emails stay in the SES mailbox.
+    env_file:
+      - path: ${HOME}/.config/thecloud/ses-smtp.env
+        required: false
    environment:
      FLOCI_SERVICES_DOCKER_NETWORK: floci_default
      FLOCI_SERVICES_RDS_PROXY_BASE_PORT: "7001"
@@ -160,7 +160,7 @@ cross-resource references.
 | Kinesis Data Firehose | `DeliveryStream` |
 | IoT Core | `DomainConfiguration` (`ServerCertificates` resolves to a JSON string), `Policy` (deleted after detaching it from its principals; on AWS the delete fails with `DeleteConflictException` while the policy is attached), `Thing`, `TopicRule` |
 | CloudFront | `CachePolicy`, `Distribution`, `OriginAccessControl`, `OriginRequestPolicy`, `ResponseHeadersPolicy` |
-| CloudWatch | `Alarm`, `Dashboard` |
+| CloudWatch | `Alarm`, `CompositeAlarm`, `Dashboard`. Composite alarms have backing definitions with name Ref and Arn GetAtt, rollback, and replacement cleanup. Composite actions are stored only; suppression properties are rejected. |
 | CloudWatch Logs | `LogGroup`, `LogStream`, `MetricFilter` |
 | WAFv2 | `WebACL` |
 | Config | `ConfigRule` |
@@ -311,6 +311,7 @@ aws logs put-retention-policy \
 | `GetMetricStatistics` | Get metric statistics (Average, Sum, etc.) |
 | `GetMetricData` | Query metrics with math expressions |
 | `PutMetricAlarm` | Create a metric alarm |
+| `PutCompositeAlarm` | Create or update a composite alarm rule |
 | `DescribeAlarms` | List alarms |
 | `DeleteAlarms` | Delete alarms |
 | `SetAlarmState` | Manually set alarm state |
@@ -331,6 +332,31 @@ aws logs put-retention-policy \
 Metric streams are stored as definitions with their `running` or `stopped` state. Floci never
 delivers metrics to the Firehose delivery stream a metric stream names.

+Composite alarms support boolean rules over alarm states. Request `AlarmTypes` containing
+`CompositeAlarm` when describing them; the default describes metric alarms. Composite
+action lists are stored but not executed. Action suppression is not implemented and is
+rejected with `ValidationError`.
+
+### SNS alarm actions
+
+State transitions publish to same-account standard SNS topics in `AlarmActions`, `OKActions`, or
+`InsufficientDataActions`, including transitions from `SetAlarmState`. Unchanged states and
+`ActionsEnabled=false` suppress notifications. Scaling action retries remain independent.
+Failures are logged per target without blocking other targets. Notifications include a
+single-metric `Trigger`; durable retries, FIFO topics, and metric-math payloads are not covered.
+
+### Metric-math alarm definitions
+
+`PutMetricAlarm` stores the `Metrics` query definitions and `DescribeAlarms` returns them over
+both JSON and Query protocols. Expressions, labels, `ReturnData`, account IDs, query periods,
+and nested metric statistics (including dimensions and units) survive storage reloads.
+Metric-math alarm responses omit the single-metric fields, including top-level `Period`.
+Updating an alarm replaces its metric definition, so changing between `Metrics` and a single
+metric does not retain the previous definition.
+
+This is management-plane support: the alarm evaluator currently evaluates only single-metric
+alarms, not metric-math expressions. `SetAlarmState` remains available for manual transitions.
+
 ### Examples

 ```bash
@@ -0,0 +1,97 @@
+package io.github.hectorvent.floci.core.common;
+
+import java.util.List;
+
+/**
+ * The message AWS's Smithy validation layer answers when a request breaks its model's constraints:
+ * "1 validation error detected: a" or "N validation errors detected: a; b", each violation reading
+ * "Value at 'path' failed to satisfy constraint: ...". The wording is Smithy's, shared by every
+ * service built on it; only the error code differs by protocol.
+ */
+public final class SmithyValidationErrors {
+
+    private SmithyValidationErrors() {}
+
+    /**
+     * The message for one or more violations. An empty list is the caller's bug, so it fails rather
+     * than answering "0 validation errors"; check {@code isEmpty()} before throwing.
+     */
+    public static String message(List<String> violations) {
+        if (violations.isEmpty()) {
+            throw new IllegalArgumentException("no violations to report");
+        }
+        String count = violations.size() == 1
+                ? "1 validation error detected: "
+                : violations.size() + " validation errors detected: ";
+        return count + String.join("; ", violations);
+    }
+
+    /** The violation for a required member the request leaves out. */
+    public static String notNull(String path) {
+        return "Value null at '" + path + "' failed to satisfy constraint: Member must not be null";
+    }
+
+    /** The 400 error carrying {@link #message} under the protocol's validation error code. */
+    public static AwsException exception(String errorCode, List<String> violations) {
+        return new AwsException(errorCode, message(violations), 400);
+    }
+
+    public static AwsException exception(String errorCode, String violation) {
+        return exception(errorCode, List.of(violation));
+    }
+
+    /** The code most JSON services use, on both the awsJson and the restJson protocols. */
+    public static AwsException validationException(List<String> violations) {
+        return exception("ValidationException", violations);
+    }
+
+    public static AwsException validationException(String violation) {
+        return validationException(List.of(violation));
+    }
+
+    /** The awsQuery protocol's code. */
+    public static AwsException validationError(List<String> violations) {
+        return exception("ValidationError", violations);
+    }
+
+    public static AwsException validationError(String violation) {
+        return validationError(List.of(violation));
+    }
+
+    /** The code of REST JSON services that model their validation failure as BadRequestException. */
+    public static AwsException badRequest(List<String> violations) {
+        return exception("BadRequestException", violations);
+    }
+
+    public static AwsException badRequest(String violation) {
+        return badRequest(List.of(violation));
+    }
+
+    /** The violation for a number outside {@code min} to {@code max}, or {@code null} for one inside. */
+    public static String outOfRange(String path, long value, long min, long max) {
+        if (value < min) {
+            return "Value '" + value + "' at '" + path + "' failed to satisfy constraint: "
+                    + "Member must have value greater than or equal to " + min;
+        }
+        if (value > max) {
+            return "Value '" + value + "' at '" + path + "' failed to satisfy constraint: "
+                    + "Member must have value less than or equal to " + max;
+        }
+        return null;
+    }
+
+    /** The violation for a value outside its enum, listing the allowed values in the model's order. */
+    public static String notInEnum(String value, String path, List<String> allowed) {
+        return "Value '" + value + "' at '" + path + "' failed to satisfy constraint: "
+                + "Member must satisfy enum value set: " + allowed;
+    }
+
+    /**
+     * The violation for a list holding a value outside its members' enum. The list is checked as a
+     * whole, so the whole list is the offending value and the enum constraint is nested.
+     */
+    public static String notAllInEnum(List<String> values, String path, List<String> allowed) {
+        return "Value '" + values + "' at '" + path + "' failed to satisfy constraint: "
+                + "Member must satisfy constraint: [Member must satisfy enum value set: " + allowed + "]";
+    }
+}
@@ -4,8 +4,10 @@ import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import io.github.hectorvent.floci.config.EmulatorConfig;
 import io.github.hectorvent.floci.core.common.SsrfProtection;
+import io.github.hectorvent.floci.services.cognito.CognitoService;
 import jakarta.annotation.PreDestroy;
 import jakarta.enterprise.context.ApplicationScoped;
+import jakarta.enterprise.inject.Instance;
 import jakarta.inject.Inject;
 import org.apache.hc.client5.http.DnsResolver;
 import org.apache.hc.client5.http.SystemDefaultDnsResolver;
@@ -37,6 +39,7 @@ import java.util.Base64;
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;

 /**
 * Verifies the RS256 signature of a token presented to an HTTP API v2 JWT authorizer, the same
@@ -66,8 +69,27 @@ public class JwtSignatureVerifier implements AutoCloseable {
    private final CloseableHttpClient httpClient;
    private final boolean allowPrivateNetworkTargets;
    private final Map<String, CachedJwks> jwksCache = new ConcurrentHashMap<>();
+    private Function<String, Optional<Map<String, RSAPublicKey>>> localIssuerKeys = issuer -> Optional.empty();

+    /**
+     * An issuer that is one of this emulator's own Cognito pools is served at Floci's base URL, which
+     * is plain HTTP on a hostname such as {@code localhost} or a Compose service name, so the HTTPS
+     * and address rules below would refuse to fetch it. Its keys are read from the pool instead:
+     * they are the same keys the pool publishes at its JWKS URL.
+     */
    @Inject
+    public JwtSignatureVerifier(ObjectMapper objectMapper, EmulatorConfig config, Instance<CognitoService> cognito) {
+        this(objectMapper, config);
+        withLocalIssuerKeys(issuer -> cognito.isResolvable()
+                ? cognito.get().localIssuerKeys(issuer) : Optional.empty());
+    }
+
+    /** Where the keys of in-process issuers come from; package-private so tests can stand one in. */
+    JwtSignatureVerifier withLocalIssuerKeys(Function<String, Optional<Map<String, RSAPublicKey>>> localIssuerKeys) {
+        this.localIssuerKeys = localIssuerKeys;
+        return this;
+    }
+
    public JwtSignatureVerifier(ObjectMapper objectMapper, EmulatorConfig config) {
        this(objectMapper, SystemDefaultDnsResolver.INSTANCE,
                config.security().allowPrivateJwtTargets());
@@ -162,6 +184,10 @@ public class JwtSignatureVerifier implements AutoCloseable {
    }

    private RSAPublicKey resolveKey(String issuer, String kid) throws JwtVerificationException {
+        Optional<Map<String, RSAPublicKey>> local = localIssuerKeys.apply(issuer);
+        if (local.isPresent()) {
+            return local.get().get(kid);
+        }
        CachedJwks cached = jwksCache.get(issuer);
        if (cached != null && !cached.isExpired()) {
            RSAPublicKey key = cached.keysByKid().get(kid);
@@ -0,0 +1,183 @@
+package io.github.hectorvent.floci.services.cloudformation.provisioners;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import io.github.hectorvent.floci.core.common.AwsException;
+import io.github.hectorvent.floci.services.cloudformation.model.StackResource;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.CloudWatchMetricsService;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
+import jakarta.enterprise.context.ApplicationScoped;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
+
+@ApplicationScoped
+public class CloudWatchCompositeAlarmCfnProvisioner implements CfnResourceProvisioner {
+    private static final String TYPE = "AWS::CloudWatch::CompositeAlarm";
+    private static final String SNAPSHOT = "FlociCompositeAlarmSnapshot";
+    private static final String TAG_KEYS = "FlociCompositeAlarmTagKeys";
+    private static final String EXPLICIT_NAME = "FlociCompositeAlarmExplicitName";
+    private static final ObjectMapper MAPPER = new ObjectMapper();
+    private final CloudWatchMetricsService service;
+
+    public CloudWatchCompositeAlarmCfnProvisioner(CloudWatchMetricsService service) {
+        this.service = service;
+    }
+
+    @Override
+    public Set<String> resourceTypes() {
+        return Set.of(TYPE);
+    }
+
+    @Override
+    public void provision(StackResource resource, JsonNode props, ProvisionContext ctx) {
+        for (String unsupported : List.of("ActionsSuppressor", "ActionsSuppressorWaitPeriod",
+                "ActionsSuppressorExtensionPeriod")) {
+            if (props.has(unsupported)) {
+                throw new AwsException("ValidationError", "Composite action suppression is not supported", 400);
+            }
+        }
+        if (resource.getAttributes().containsKey(SNAPSHOT)) {
+            throw new AwsException("ResourceConflictException", "Alarm update cleanup is still pending", 400);
+        }
+        String explicit = ctx.resolveOptional(props, "AlarmName");
+        boolean removedName = explicit == null && "true".equals(resource.getAttributes().get(EXPLICIT_NAME));
+        String name = removedName ? ctx.generatePhysicalName(resource.getLogicalId(), 255, false)
+                : ctx.stablePhysicalName(explicit, resource.getLogicalId(), 255, false);
+        CompositeAlarm alarm = new CompositeAlarm();
+        alarm.setAlarmName(name);
+        alarm.setAlarmDescription(ctx.resolveOptional(props, "AlarmDescription"));
+        alarm.setAlarmRule(ctx.resolveOptional(props, "AlarmRule"));
+        alarm.setActionsEnabled(!"false".equals(ctx.resolveOptional(props, "ActionsEnabled")));
+        alarm.setTags(ctx.resolveTags(props, "Tags"));
+        actions(props, "AlarmActions", ctx, alarm.getAlarmActions());
+        actions(props, "OKActions", ctx, alarm.getOkActions());
+        actions(props, "InsufficientDataActions", ctx, alarm.getInsufficientDataActions());
+        Map<String, String> desiredTags = Map.copyOf(alarm.getTags());
+        Map<String, String> priorAttributes = Map.copyOf(resource.getAttributes());
+        boolean inPlace = ctx.reusesPriorEntity(name);
+        String updateSnapshot = null;
+        if (inPlace) {
+            ObjectNode snapshot = MAPPER.createObjectNode().put("region", ctx.region()).put("name", name);
+            List<CompositeAlarm> previous = service.describeCompositeAlarms(List.of(name), null, ctx.region());
+            if (!previous.isEmpty()) {
+                snapshot.set("alarm", MAPPER.valueToTree(previous.getFirst()));
+            }
+            snapshot.set("attributes", MAPPER.valueToTree(priorAttributes));
+            Set<String> changedKeys = new TreeSet<>(desiredTags.keySet());
+            changedKeys.addAll(tagKeys(resource.getAttributes().get(TAG_KEYS)));
+            snapshot.set("changedTagKeys", MAPPER.valueToTree(changedKeys));
+            updateSnapshot = snapshot.toString();
+        }
+        service.putCompositeAlarm(alarm, ctx.region(), inPlace);
+        if (inPlace) {
+            resource.getAttributes().put(SNAPSHOT, updateSnapshot);
+            reconcileTags(alarm.getAlarmArn(), tagKeys(priorAttributes.get(TAG_KEYS)), desiredTags, ctx.region());
+        }
+        resource.getAttributes().put(TAG_KEYS, MAPPER.valueToTree(desiredTags.keySet()).toString());
+        resource.setPhysicalId(name);
+        resource.getAttributes().put("Arn", alarm.getAlarmArn());
+        resource.getAttributes().put(EXPLICIT_NAME, Boolean.toString(explicit != null));
+        ReplacementCleanup.record(resource, ctx, priorAttributes);
+    }
+
+    private static void actions(JsonNode props, String field, ProvisionContext ctx, List<String> target) {
+        JsonNode values = ctx.engine().resolveNode(props.path(field));
+        if (values != null && values.isArray()) {
+            values.forEach(value -> target.add(value.asText()));
+        }
+    }
+
+    private static Set<String> tagKeys(String json) {
+        Set<String> keys = new TreeSet<>();
+        if (json != null) {
+            try {
+                MAPPER.readTree(json).forEach(value -> keys.add(value.asText()));
+            } catch (JsonProcessingException error) {
+                throw new IllegalStateException("Cannot read composite alarm tag ownership", error);
+            }
+        }
+        return keys;
+    }
+
+    private void reconcileTags(String arn, Set<String> owned, Map<String, String> desired, String region) {
+        List<String> removed = owned.stream().filter(key -> !desired.containsKey(key)).toList();
+        if (!removed.isEmpty()) {
+            service.untagResource(arn, removed, region);
+        }
+        if (!desired.isEmpty()) {
+            service.tagResource(arn, desired, region);
+        }
+    }
+
+    @Override
+    public void delete(String type, String physicalId, String region) {
+        service.deleteAlarms(List.of(physicalId), region);
+    }
+
+    @Override
+    public boolean retainsFailedUpdateState(StackResource resource) {
+        return resource.getAttributes().containsKey(SNAPSHOT);
+    }
+
+    @Override
+    public boolean rollbackUpdate(StackResource resource) {
+        if (ReplacementCleanup.rollback(resource, this::delete)) {
+            return true;
+        }
+        String raw = resource.getAttributes().get(SNAPSHOT);
+        if (raw == null) {
+            return false;
+        }
+        try {
+            JsonNode snapshot = MAPPER.readTree(raw);
+            String region = snapshot.path("region").asText();
+            if (snapshot.has("alarm")) {
+                CompositeAlarm original = MAPPER.treeToValue(snapshot.get("alarm"), CompositeAlarm.class);
+                Map<String, String> originalTags = Map.copyOf(original.getTags());
+                service.putCompositeAlarm(original, region);
+                Set<String> changed = tagKeys(snapshot.path("changedTagKeys").toString());
+                reconcileTags(original.getAlarmArn(), changed, originalTags.entrySet().stream()
+                        .filter(entry -> changed.contains(entry.getKey()))
+                        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)), region);
+            } else {
+                delete(TYPE, snapshot.path("name").asText(), region);
+            }
+            resource.getAttributes().clear();
+            snapshot.path("attributes").fields().forEachRemaining(entry ->
+                    resource.getAttributes().put(entry.getKey(), entry.getValue().asText()));
+        } catch (JsonProcessingException error) {
+            throw new IllegalStateException("Cannot read composite alarm rollback state", error);
+        }
+        return true;
+    }
+
+    @Override
+    public boolean hasReplacementUpdate(StackResource resource) {
+        return ReplacementCleanup.hasReplacement(resource);
+    }
+
+    @Override
+    public String updateCleanupPhysicalId(StackResource resource) {
+        return ReplacementCleanup.cleanupPhysicalId(resource);
+    }
+
+    @Override
+    public UpdateCleanupResult completeUpdate(StackResource resource) {
+        if (resource.getAttributes().containsKey(SNAPSHOT) && !ReplacementCleanup.hasReplacement(resource)) {
+            return new UpdateCleanupResult(true, true, null, 0, null);
+        }
+        return ReplacementCleanup.complete(resource, this::delete);
+    }
+
+    @Override
+    public void clearUpdate(StackResource resource) {
+        resource.getAttributes().remove(SNAPSHOT);
+        ReplacementCleanup.clear(resource);
+    }
+}
@@ -9,9 +9,11 @@ import io.github.hectorvent.floci.services.cloudformation.model.StackResource;
 import org.jboss.logging.Logger;

 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;

 /**
 * The replacement lifecycle for provisioners whose replacing update simply creates the new entity
@@ -121,6 +123,22 @@ public final class ReplacementCleanup {
        return cleanup != null && cleanup.path("displaced").size() > 0;
    }

+    /** The physical IDs of replaced resources this resource still has to delete. */
+    static Set<String> owedPhysicalIds(StackResource r) {
+        Set<String> owed = new HashSet<>();
+        ObjectNode cleanup = read(r);
+        if (cleanup == null) {
+            return owed;
+        }
+        for (JsonNode entry : cleanup.path("displaced")) {
+            String physicalId = entry.path("physicalId").asText(null);
+            if (physicalId != null) {
+                owed.add(physicalId);
+            }
+        }
+        return owed;
+    }
+
    /**
     * The entity the cleanup is working on, or null when none is owed or {@code UpdateReplacePolicy:
     * Retain} keeps it. The engine announces one physical id per resource, so a resource owing more
@@ -179,29 +179,82 @@ public class CloudWatchDashboardsService {
    }

    public Map<String, String> listTagsForResource(String resourceArn, String region) {
-        return findByArn(resourceArn, region).map(Dashboard::getTags).orElse(Map.of());
+        return requireDashboard(resourceArn, region).getTags();
    }

    public void tagResource(String resourceArn, Map<String, String> tags, String region) {
-        findByArn(resourceArn, region).ifPresent(dashboard -> {
-            dashboard.getTags().putAll(tags);
-            dashboardStore.put(key(region, dashboard.getDashboardName()), dashboard);
-        });
+        Dashboard dashboard = requireDashboard(resourceArn, region);
+        dashboard.getTags().putAll(tags);
+        dashboardStore.put(key(region, dashboard.getDashboardName()), dashboard);
    }

    public void untagResource(String resourceArn, List<String> tagKeys, String region) {
-        findByArn(resourceArn, region).ifPresent(dashboard -> {
-            tagKeys.forEach(dashboard.getTags()::remove);
-            dashboardStore.put(key(region, dashboard.getDashboardName()), dashboard);
-        });
+        Dashboard dashboard = requireDashboard(resourceArn, region);
+        tagKeys.forEach(dashboard.getTags()::remove);
+        dashboardStore.put(key(region, dashboard.getDashboardName()), dashboard);
+    }
+
+    /**
+     * Resolves the dashboard an ARN names, or reports that nothing does. The tag operations
+     * declare {@code ResourceNotFoundException}, which is a different shape from the
+     * {@code ResourceNotFound} that {@code GetDashboard} declares,
+     * so this is not the {@link #notFound(String)} used by the rest of this service.
+     */
+    private Dashboard requireDashboard(String resourceArn, String region) {
+        return findByArn(resourceArn, region).orElseThrow(() ->
+                new AwsException("ResourceNotFoundException",
+                        "Dashboard does not exist: " + resourceArn, 404));
    }

    private java.util.Optional<Dashboard> findByArn(String resourceArn, String region) {
        return dashboardStore.scan(k -> k.startsWith(region + "::")).stream()
-                .filter(d -> d.getDashboardArn() != null && d.getDashboardArn().equals(resourceArn))
+                .filter(d -> namesDashboard(resourceArn, d.getDashboardArn()))
                .findFirst();
    }

+    /**
+     * Whether {@code candidate} is an ARN for the dashboard whose own ARN is {@code stored}.
+     *
+     * <p>Both the region-ful and the regionless form resolve, deliberately, because the two
+     * disagree here and a caller may hold either. Dashboards are a global resource and AWS
+     * documents their ARN without a region on both the TagResource and the ListTagsForResource
+     * pages, {@code arn:aws:cloudwatch::<account-id>:dashboard/<dashboard-name>}, while Floci
+     * mints a region-ful one. That divergence used to be invisible on this path: an ARN
+     * matching nothing was a silent success answering an empty tag map. Now that it is an
+     * error, a caller sending the documented ARN for a dashboard that exists would be told the
+     * dashboard does not, so the lookup accepts both shapes.
+     *
+     * <p>What Floci mints is left alone here on purpose. Clients may already hold the ARNs it
+     * has handed out, so bringing the minted shape into line with AWS is a separate change
+     * from making the lookup tolerant, and only the second one is needed to keep this path
+     * correct.
+     *
+     * <p>Only an absent region is accepted in place of the dashboard's own, so an ARN naming
+     * some other region is still a miss rather than resolving to a same-named dashboard
+     * elsewhere.
+     */
+    private static boolean namesDashboard(String candidate, String stored) {
+        if (candidate == null || stored == null) {
+            return false;
+        }
+        return candidate.equals(stored) || candidate.equals(withoutRegion(stored));
+    }
+
+    /**
+     * Blanks the region field of an ARN, turning
+     * {@code arn:aws:cloudwatch:us-east-1:123:dashboard/x} into
+     * {@code arn:aws:cloudwatch::123:dashboard/x}. An ARN with fewer than six fields is
+     * returned unchanged, since there is no region field to blank.
+     */
+    private static String withoutRegion(String arn) {
+        String[] fields = arn.split(":", 6);
+        if (fields.length < 6) {
+            return arn;
+        }
+        fields[3] = "";
+        return String.join(":", fields);
+    }
+
    private static String key(String region, String dashboardName) {
        return region + "::" + dashboardName;
    }
@@ -275,9 +275,10 @@ public class AlarmEvaluator {

    private static boolean isEvaluable(MetricAlarm alarm) {
        return alarm.getRegion() != null
+                && alarm.getMetrics().isEmpty()
                && alarm.getNamespace() != null && !alarm.getNamespace().isBlank()
                && alarm.getMetricName() != null && !alarm.getMetricName().isBlank()
-                && alarm.getPeriod() > 0
+                && alarm.getPeriod() != null && alarm.getPeriod() > 0
                && alarm.getEvaluationPeriods() > 0
                && alarm.getComparisonOperator() != null;
    }
@@ -0,0 +1,155 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.core.common.AwsArnUtils;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.services.sns.SnsService;
+import jakarta.enterprise.context.ApplicationScoped;
+import org.jboss.logging.Logger;
+
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+
+/** Publishes SNS actions once per state transition, independently of scaling action retries. */
+@ApplicationScoped
+public class AlarmSnsNotifier {
+
+    /** The names CloudWatch writes in the alarm message's Region field; other regions use their ID. */
+    private static final Map<String, String> REGION_NAMES = Map.ofEntries(
+            Map.entry("us-east-1", "US East (N. Virginia)"),
+            Map.entry("us-east-2", "US East (Ohio)"),
+            Map.entry("us-west-1", "US West (N. California)"),
+            Map.entry("us-west-2", "US West (Oregon)"),
+            Map.entry("ca-central-1", "Canada (Central)"),
+            Map.entry("ca-west-1", "Canada West (Calgary)"),
+            Map.entry("sa-east-1", "South America (Sao Paulo)"),
+            Map.entry("eu-west-1", "EU (Ireland)"),
+            Map.entry("eu-west-2", "EU (London)"),
+            Map.entry("eu-west-3", "EU (Paris)"),
+            Map.entry("eu-central-1", "EU (Frankfurt)"),
+            Map.entry("eu-central-2", "EU (Zurich)"),
+            Map.entry("eu-north-1", "EU (Stockholm)"),
+            Map.entry("eu-south-1", "EU (Milan)"),
+            Map.entry("eu-south-2", "EU (Spain)"),
+            Map.entry("me-south-1", "Middle East (Bahrain)"),
+            Map.entry("me-central-1", "Middle East (UAE)"),
+            Map.entry("il-central-1", "Israel (Tel Aviv)"),
+            Map.entry("af-south-1", "Africa (Cape Town)"),
+            Map.entry("ap-east-1", "Asia Pacific (Hong Kong)"),
+            Map.entry("ap-south-1", "Asia Pacific (Mumbai)"),
+            Map.entry("ap-south-2", "Asia Pacific (Hyderabad)"),
+            Map.entry("ap-northeast-1", "Asia Pacific (Tokyo)"),
+            Map.entry("ap-northeast-2", "Asia Pacific (Seoul)"),
+            Map.entry("ap-northeast-3", "Asia Pacific (Osaka)"),
+            Map.entry("ap-southeast-1", "Asia Pacific (Singapore)"),
+            Map.entry("ap-southeast-2", "Asia Pacific (Sydney)"),
+            Map.entry("ap-southeast-3", "Asia Pacific (Jakarta)"),
+            Map.entry("ap-southeast-4", "Asia Pacific (Melbourne)"));
+
+    private static final Logger LOG = Logger.getLogger(AlarmSnsNotifier.class);
+    private static final DateTimeFormatter TIMESTAMP_FORMAT = DateTimeFormatter
+            .ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ", Locale.ROOT).withZone(ZoneOffset.UTC);
+    private final SnsService snsService;
+    private final ObjectMapper objectMapper;
+
+    public AlarmSnsNotifier(SnsService snsService, ObjectMapper objectMapper) {
+        this.snsService = snsService;
+        this.objectMapper = objectMapper;
+    }
+
+    record Notification(String topicArn, String message, String subject, String region) {}
+
+    List<Notification> prepareTransition(MetricAlarm alarm, String oldState) {
+        if (!alarm.isActionsEnabled() || alarm.getStateValue().equals(oldState)) {
+            return List.of();
+        }
+        List<String> actions = switch (alarm.getStateValue()) {
+            case "ALARM" -> alarm.getAlarmActions();
+            case "OK" -> alarm.getOkActions();
+            case "INSUFFICIENT_DATA" -> alarm.getInsufficientDataActions();
+            default -> List.of();
+        };
+        if (actions == null) {
+            return List.of();
+        }
+        List<Notification> notifications = new ArrayList<>();
+        for (String action : actions) {
+            if (!AwsArnUtils.isArnFor(action, "sns")) {
+                continue;
+            }
+            try {
+                AwsArnUtils.Arn topic = AwsArnUtils.parse(action);
+                String subject = alarm.getStateValue() + ": \"" + alarm.getAlarmName() + "\"";
+                if (subject.length() > 100) {
+                    subject = subject.substring(0, 100);
+                }
+                notifications.add(new Notification(action, message(alarm, oldState), subject, topic.region()));
+            } catch (Exception e) {
+                LOG.warnv(e, "Unable to publish alarm {0} state {1} to SNS action {2}",
+                        alarm.getAlarmName(), alarm.getStateValue(), action);
+            }
+        }
+        return notifications;
+    }
+
+    void publish(List<Notification> notifications) {
+        for (Notification notification : notifications) {
+            try {
+                snsService.publish(notification.topicArn(), null, notification.message(),
+                        notification.subject(), notification.region());
+            } catch (Exception error) {
+                LOG.warnv(error, "Unable to publish alarm transition {0} to SNS action {1}",
+                        notification.subject(), notification.topicArn());
+            }
+        }
+    }
+
+    private String message(MetricAlarm alarm, String oldState) throws JsonProcessingException {
+        AwsArnUtils.Arn arn = AwsArnUtils.parse(alarm.getAlarmArn());
+        Map<String, Object> payload = new LinkedHashMap<>();
+        payload.put("AlarmName", alarm.getAlarmName());
+        payload.put("AlarmDescription", alarm.getAlarmDescription());
+        payload.put("AWSAccountId", arn.accountId());
+        payload.put("AlarmConfigurationUpdatedTimestamp", timestamp(alarm.getAlarmConfigurationUpdatedTimestamp()));
+        payload.put("NewStateValue", alarm.getStateValue());
+        payload.put("NewStateReason", alarm.getStateReason());
+        payload.put("StateChangeTime", timestamp(alarm.getStateUpdatedTimestamp()));
+        payload.put("Region", REGION_NAMES.getOrDefault(arn.region(), arn.region()));
+        payload.put("AlarmArn", alarm.getAlarmArn());
+        payload.put("OldStateValue", oldState);
+        payload.put("OKActions", alarm.getOkActions());
+        payload.put("AlarmActions", alarm.getAlarmActions());
+        payload.put("InsufficientDataActions", alarm.getInsufficientDataActions());
+        Map<String, Object> trigger = new LinkedHashMap<>();
+        trigger.put("MetricName", alarm.getMetricName());
+        trigger.put("Namespace", alarm.getNamespace());
+        trigger.put("StatisticType", "Statistic");
+        trigger.put("Statistic", alarm.getStatistic() != null
+                ? alarm.getStatistic().toUpperCase(Locale.ROOT) : null);
+        trigger.put("Unit", alarm.getUnit());
+        trigger.put("Dimensions", alarm.getDimensions());
+        trigger.put("Period", alarm.getPeriod());
+        trigger.put("EvaluationPeriods", alarm.getEvaluationPeriods());
+        if (alarm.getDatapointsToAlarm() != null) {
+            trigger.put("DatapointsToAlarm", alarm.getDatapointsToAlarm());
+        }
+        trigger.put("ComparisonOperator", alarm.getComparisonOperator());
+        trigger.put("Threshold", alarm.getThreshold());
+        trigger.put("TreatMissingData", alarm.getTreatMissingData());
+        trigger.put("EvaluateLowSampleCountPercentile", alarm.getEvaluateLowSampleCountPercentile() != null
+                ? alarm.getEvaluateLowSampleCountPercentile() : "");
+        payload.put("Trigger", trigger);
+        return objectMapper.writeValueAsString(payload);
+    }
+
+    private String timestamp(long epochSeconds) {
+        return TIMESTAMP_FORMAT.format(Instant.ofEpochSecond(epochSeconds));
+    }
+}
@@ -0,0 +1,34 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import io.github.hectorvent.floci.core.common.AwsException;
+
+/**
+ * A CloudWatch error whose Query code and JSON shape name differ.
+ *
+ * <p>CloudWatch is awsQueryCompatible: the Query {@code <Code>} and the
+ * {@code x-amzn-query-error} header carry the {@code awsQueryError} code
+ * ({@code MissingParameter}), while a JSON 1.0 or CBOR body's {@code __type} names the
+ * model shape ({@code MissingRequiredParameterException}). The AWS SDK v2 picks the typed
+ * exception from {@code __type}, so the code alone yields a generic {@code CloudWatchException}.
+ * Keeping {@link #getErrorCode()} as the Query code and overriding {@link #jsonType()}
+ * reproduces both surfaces.
+ */
+class CloudWatchMetricsException extends AwsException {
+
+    private final String jsonType;
+
+    private CloudWatchMetricsException(String errorCode, String jsonType, String message, int httpStatus) {
+        super(errorCode, message, httpStatus);
+        this.jsonType = jsonType;
+    }
+
+    static CloudWatchMetricsException missingParameter(String parameter) {
+        return new CloudWatchMetricsException("MissingParameter", "MissingRequiredParameterException",
+                "The parameter " + parameter + " is required.", 400);
+    }
+
+    @Override
+    public String jsonType() {
+        return jsonType;
+    }
+}
@@ -5,13 +5,21 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import io.github.hectorvent.floci.core.common.AwsErrorResponse;
+import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.core.common.PaginatedResult;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.model.Dashboard;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.AlarmMetricDataQuery;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Dimension;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.CloudWatchMetricStreamsService;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStream;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStreamFilter;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStreamStatisticsConfiguration;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.AlarmMetricDataQuery;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Dimension;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
@@ -56,6 +64,7 @@ public class CloudWatchMetricsJsonHandler {
            case "ListMetrics" -> handleListMetrics(request, region);
            case "GetMetricStatistics" -> handleGetMetricStatistics(request, region);
            case "PutMetricAlarm" -> handlePutMetricAlarm(request, region);
+            case "PutCompositeAlarm" -> handlePutCompositeAlarm(request, region);
            case "DescribeAlarms" -> handleDescribeAlarms(request, region);
            case "DeleteAlarms" -> handleDeleteAlarms(request, region);
            case "SetAlarmState" -> handleSetAlarmState(request, region);
@@ -81,10 +90,14 @@ public class CloudWatchMetricsJsonHandler {

    private Response handlePutMetricData(JsonNode request, String region) {
        String namespace = request.path("Namespace").asText();
-        LOG.infov("JSON PutMetricData raw: {0}", request);
-        List<MetricDatum> datums = parseMetricDataJson(request.path("MetricData"));
-        LOG.infov("JSON PutMetricData parsed {0} datums, sums={1}", datums.size(),
-                datums.stream().map(d -> d.getMetricName() + "=" + d.getSum()).toList());
+        List<MetricDatum> datums = parseMetricDataJson(request.path("MetricData"), "MetricData");
+        int entityIndex = 0;
+        for (JsonNode entityMetricData : request.path("EntityMetricData")) {
+            entityIndex++;
+            datums.addAll(parseMetricDataJson(entityMetricData.path("MetricData"),
+                    "EntityMetricData.member." + entityIndex + ".MetricData"));
+        }
+        LOG.debugv("JSON PutMetricData parsed {0} datums for namespace {1}", datums.size(), namespace);
        metricsService.putMetricData(namespace, datums, region);
        return Response.ok(objectMapper.createObjectNode()).build();
    }
@@ -151,12 +164,17 @@ public class CloudWatchMetricsJsonHandler {

    private Response handlePutMetricAlarm(JsonNode request, String region) {
        MetricAlarm alarm = new MetricAlarm();
-        alarm.setAlarmName(request.path("AlarmName").asText());
-        alarm.setAlarmDescription(request.path("AlarmDescription").asText(null));
+        parseAlarmFields(request, alarm);
        alarm.setMetricName(request.path("MetricName").asText(null));
        alarm.setNamespace(request.path("Namespace").asText(null));
        alarm.setStatistic(request.path("Statistic").asText(null));
-        alarm.setPeriod(request.path("Period").asInt(60));
+        JsonNode metrics = request.path("Metrics");
+        if (metrics.isArray()) {
+            for (JsonNode query : metrics) {
+                alarm.getMetrics().add(objectMapper.convertValue(query, AlarmMetricDataQuery.class));
+            }
+        }
+        alarm.setPeriod(alarm.getMetrics().isEmpty() ? request.path("Period").asInt(60) : null);
        alarm.setUnit(request.path("Unit").asText(null));
        alarm.setEvaluationPeriods(request.path("EvaluationPeriods").asInt(1));
        alarm.setDatapointsToAlarm(request.hasNonNull("DatapointsToAlarm")
@@ -164,9 +182,33 @@ public class CloudWatchMetricsJsonHandler {
        alarm.setThreshold(request.path("Threshold").asDouble(0));
        alarm.setComparisonOperator(request.path("ComparisonOperator").asText(null));
        alarm.setTreatMissingData(request.path("TreatMissingData").asText(null));
-        alarm.setActionsEnabled(request.path("ActionsEnabled").asBoolean(true));
        alarm.setDimensions(parseDimensionsJson(request.path("Dimensions")));

+        metricsService.putMetricAlarm(alarm, region);
+        return Response.ok(objectMapper.createObjectNode()).build();
+    }
+
+    private Response handlePutCompositeAlarm(JsonNode request, String region) {
+        rejectSuppressor(request);
+        CompositeAlarm alarm = new CompositeAlarm();
+        parseAlarmFields(request, alarm);
+        alarm.setAlarmRule(request.path("AlarmRule").asText(null));
+        metricsService.putCompositeAlarm(alarm, region);
+        return Response.ok(objectMapper.createObjectNode()).build();
+    }
+
+    private static void rejectSuppressor(JsonNode request) {
+        if (request.has("ActionsSuppressor") || request.has("ActionsSuppressorWaitPeriod")
+                || request.has("ActionsSuppressorExtensionPeriod")) {
+            throw new AwsException("ValidationError", "Composite action suppression is not supported", 400);
+        }
+    }
+
+    private void parseAlarmFields(JsonNode request, Alarm alarm) {
+        alarm.setAlarmName(request.path("AlarmName").asText());
+        alarm.setAlarmDescription(request.path("AlarmDescription").asText(null));
+        alarm.setActionsEnabled(request.path("ActionsEnabled").asBoolean(true));
+
        JsonNode alarmActions = request.path("AlarmActions");
        if (alarmActions.isArray()) {
            alarmActions.forEach(a -> alarm.getAlarmActions().add(a.asText()));
@@ -187,8 +229,6 @@ public class CloudWatchMetricsJsonHandler {
            alarm.setTags(tags);
        }

-        metricsService.putMetricAlarm(alarm, region);
-        return Response.ok(objectMapper.createObjectNode()).build();
    }

    private Response handleDescribeAlarms(JsonNode request, String region) {
@@ -199,32 +239,42 @@ public class CloudWatchMetricsJsonHandler {
        }
        String prefix = request.has("AlarmNamePrefix") ? request.path("AlarmNamePrefix").asText() : null;

-        List<MetricAlarm> alarms = metricsService.describeAlarms(alarmNames, prefix, region);
+        List<String> types = new ArrayList<>();
+        request.path("AlarmTypes").forEach(value -> types.add(value.asText()));
+        metricsService.validateAlarmTypes(types);
+        List<MetricAlarm> alarms = types.isEmpty() || types.contains("MetricAlarm")
+                ? metricsService.describeAlarms(alarmNames, prefix, region) : List.of();

        ObjectNode response = objectMapper.createObjectNode();
        ArrayNode arr = response.putArray("MetricAlarms");
        for (MetricAlarm a : alarms) {
            ObjectNode node = arr.addObject();
-            node.put("AlarmName", a.getAlarmName());
-            if (a.getAlarmArn() != null) node.put("AlarmArn", a.getAlarmArn());
-            if (a.getAlarmDescription() != null) node.put("AlarmDescription", a.getAlarmDescription());
-            ArrayNode alarmActions = node.putArray("AlarmActions");
-            a.getAlarmActions().forEach(alarmActions::add);
-            ArrayNode okActions = node.putArray("OKActions");
-            a.getOkActions().forEach(okActions::add);
-            ArrayNode insufficientDataActions = node.putArray("InsufficientDataActions");
-            a.getInsufficientDataActions().forEach(insufficientDataActions::add);
-            if (a.getMetricName() != null) node.put("MetricName", a.getMetricName());
-            if (a.getNamespace() != null) node.put("Namespace", a.getNamespace());
-            if (a.getStatistic() != null) node.put("Statistic", a.getStatistic());
-            ArrayNode dimensions = node.putArray("Dimensions");
-            a.getDimensions().forEach(d -> {
-                ObjectNode dimNode = dimensions.addObject();
-                dimNode.put("Name", d.name());
-                dimNode.put("Value", d.value());
-            });
-            node.put("Period", a.getPeriod());
-            if (a.getUnit() != null) node.put("Unit", a.getUnit());
+            describeAlarmFields(node, a);
+            if (!a.getMetrics().isEmpty()) {
+                node.set("Metrics", objectMapper.valueToTree(a.getMetrics()));
+            } else {
+                if (a.getMetricName() != null) {
+                    node.put("MetricName", a.getMetricName());
+                }
+                if (a.getNamespace() != null) {
+                    node.put("Namespace", a.getNamespace());
+                }
+                if (a.getStatistic() != null) {
+                    node.put("Statistic", a.getStatistic());
+                }
+                ArrayNode dimensions = node.putArray("Dimensions");
+                a.getDimensions().forEach(d -> {
+                    ObjectNode dimNode = dimensions.addObject();
+                    dimNode.put("Name", d.name());
+                    dimNode.put("Value", d.value());
+                });
+                if (a.getPeriod() != null) {
+                    node.put("Period", a.getPeriod());
+                }
+                if (a.getUnit() != null) {
+                    node.put("Unit", a.getUnit());
+                }
+            }
            node.put("EvaluationPeriods", a.getEvaluationPeriods());
            if (a.getDatapointsToAlarm() != null) {
                node.put("DatapointsToAlarm", a.getDatapointsToAlarm());
@@ -232,15 +282,48 @@ public class CloudWatchMetricsJsonHandler {
            node.put("Threshold", a.getThreshold());
            if (a.getComparisonOperator() != null) node.put("ComparisonOperator", a.getComparisonOperator());
            if (a.getTreatMissingData() != null) node.put("TreatMissingData", a.getTreatMissingData());
-            node.put("ActionsEnabled", a.isActionsEnabled());
-            if (a.getStateValue() != null) node.put("StateValue", a.getStateValue());
-            if (a.getStateReason() != null) node.put("StateReason", a.getStateReason());
-            if (a.getStateReasonData() != null) node.put("StateReasonData", a.getStateReasonData());
-            node.put("StateUpdatedTimestamp", a.getStateUpdatedTimestamp());
+
        }
+        ArrayNode composites = response.putArray("CompositeAlarms");
+        if (types.contains("CompositeAlarm")) {
+            for (CompositeAlarm alarm : metricsService.describeCompositeAlarms(alarmNames, prefix, region)) {
+                ObjectNode node = composites.addObject();
+                describeAlarmFields(node, alarm);
+                node.put("AlarmRule", alarm.getAlarmRule());
+            }
+        }
+        response.putArray("LogAlarms");
        return Response.ok(response).build();
    }

+    private void describeAlarmFields(ObjectNode node, Alarm a) {
+        node.put("AlarmName", a.getAlarmName());
+        if (a.getAlarmArn() != null) {
+            node.put("AlarmArn", a.getAlarmArn());
+        }
+        if (a.getAlarmDescription() != null) {
+            node.put("AlarmDescription", a.getAlarmDescription());
+        }
+        ArrayNode alarmActions = node.putArray("AlarmActions");
+        a.getAlarmActions().forEach(alarmActions::add);
+        ArrayNode okActions = node.putArray("OKActions");
+        a.getOkActions().forEach(okActions::add);
+        ArrayNode insufficientDataActions = node.putArray("InsufficientDataActions");
+        a.getInsufficientDataActions().forEach(insufficientDataActions::add);
+        node.put("ActionsEnabled", a.isActionsEnabled());
+        if (a.getStateValue() != null) {
+            node.put("StateValue", a.getStateValue());
+        }
+        if (a.getStateReason() != null) {
+            node.put("StateReason", a.getStateReason());
+        }
+        if (a.getStateReasonData() != null) {
+            node.put("StateReasonData", a.getStateReasonData());
+        }
+        node.put("StateUpdatedTimestamp", a.getStateUpdatedTimestamp());
+        node.put("AlarmConfigurationUpdatedTimestamp", a.getAlarmConfigurationUpdatedTimestamp());
+    }
+
    private Response handleDeleteAlarms(JsonNode request, String region) {
        List<String> alarmNames = new ArrayList<>();
        JsonNode namesNode = request.path("AlarmNames");
@@ -586,12 +669,18 @@ public class CloudWatchMetricsJsonHandler {
        return configurations;
    }

-    private List<MetricDatum> parseMetricDataJson(JsonNode node) {
+    private List<MetricDatum> parseMetricDataJson(JsonNode node, String listPath) {
        List<MetricDatum> datums = new ArrayList<>();
        if (!node.isArray()) return datums;
+        int index = 0;
        for (JsonNode item : node) {
+            index++;
+            JsonNode metricName = item.path("MetricName");
+            if (!metricName.isTextual() || metricName.asText().isEmpty()) {
+                throw CloudWatchMetricsException.missingParameter(listPath + ".member." + index + ".MetricName");
+            }
            MetricDatum datum = new MetricDatum();
-            datum.setMetricName(item.path("MetricName").asText());
+            datum.setMetricName(metricName.asText());
            datum.setValue(item.path("Value").asDouble(0));
            datum.setUnit(item.path("Unit").asText(null));
            JsonNode ts = item.path("Timestamp");
@@ -1,5 +1,6 @@
 package io.github.hectorvent.floci.services.cloudwatch.metrics;

+import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.core.common.AwsNamespaces;
 import io.github.hectorvent.floci.core.common.AwsQueryResponse;
 import io.github.hectorvent.floci.core.common.PaginatedResult;
@@ -7,10 +8,17 @@ import io.github.hectorvent.floci.core.common.Pagination;
 import io.github.hectorvent.floci.core.common.XmlBuilder;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.model.Dashboard;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.AlarmMetricDataQuery;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Dimension;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.CloudWatchMetricStreamsService;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStream;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStreamFilter;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.model.MetricStreamStatisticsConfiguration;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.AlarmMetricDataQuery;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Dimension;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
@@ -25,11 +33,16 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import org.jboss.logging.Logger;
+import java.util.SortedSet;
+import java.util.TreeSet;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;

@ApplicationScoped
 public class CloudWatchMetricsQueryHandler {

    private static final Logger LOG = Logger.getLogger(CloudWatchMetricsQueryHandler.class);
+    private static final Pattern ENTITY_METRIC_DATA_MEMBER = Pattern.compile("EntityMetricData\\.member\\.(\\d{1,9})\\.");

    private CloudWatchMetricsService metricsService;
    private final CloudWatchDashboardsService dashboardsService;
@@ -52,6 +65,7 @@ public class CloudWatchMetricsQueryHandler {
            case "GetMetricStatistics" -> handleGetMetricStatistics(params, region);
            case "GetMetricData" -> handleGetMetricData(params, region);
            case "PutMetricAlarm" -> handlePutMetricAlarm(params, region);
+            case "PutCompositeAlarm" -> handlePutCompositeAlarm(params, region);
            case "DescribeAlarms" -> handleDescribeAlarms(params, region);
            case "DeleteAlarms" -> handleDeleteAlarms(params, region);
            case "SetAlarmState" -> handleSetAlarmState(params, region);
@@ -153,7 +167,8 @@ public class CloudWatchMetricsQueryHandler {
            xml.elem("Unit", dp.unit()).end("member");
        }
        xml.end("Datapoints");
-        return Response.ok(AwsQueryResponse.envelope("GetMetricStatistics", AwsNamespaces.CW, xml.build())).build();
+        return Response.ok(AwsQueryResponse.envelope("GetMetricStatistics",
+                AwsNamespaces.CW, xml.build())).build();
    }

    private Response handleGetMetricData(MultivaluedMap<String, String> params, String region) {
@@ -237,6 +252,26 @@ public class CloudWatchMetricsQueryHandler {
        return Response.ok(AwsQueryResponse.envelopeNoResult("PutMetricAlarm", null)).build();
    }

+    private Response handlePutCompositeAlarm(MultivaluedMap<String, String> params, String region) {
+        if (params.containsKey("ActionsSuppressor") || params.containsKey("ActionsSuppressorWaitPeriod")
+                || params.containsKey("ActionsSuppressorExtensionPeriod")) {
+            throw new AwsException("ValidationError", "Composite action suppression is not supported", 400);
+        }
+        CompositeAlarm alarm = new CompositeAlarm();
+        parseAlarmFields(params, alarm);
+        alarm.setAlarmRule(params.getFirst("AlarmRule"));
+        metricsService.putCompositeAlarm(alarm, region);
+        return Response.ok(AwsQueryResponse.envelopeNoResult("PutCompositeAlarm", null)).build();
+    }
+
+    private static List<String> alarmMembers(MultivaluedMap<String, String> params, String key) {
+        List<String> values = new ArrayList<>();
+        for (int i = 1; params.getFirst(key + ".member." + i) != null; i++) {
+            values.add(params.getFirst(key + ".member." + i));
+        }
+        return values;
+    }
+
    private Response handleDescribeAlarms(MultivaluedMap<String, String> params, String region) {
        List<String> alarmNames = new ArrayList<>();
        for (int i = 1; ; i++) {
@@ -246,13 +281,24 @@ public class CloudWatchMetricsQueryHandler {
        }
        String prefix = params.getFirst("AlarmNamePrefix");

-        List<MetricAlarm> alarms = metricsService.describeAlarms(alarmNames, prefix, region);
+        List<String> types = alarmMembers(params, "AlarmTypes");
+        metricsService.validateAlarmTypes(types);
+        List<MetricAlarm> alarms = types.isEmpty() || types.contains("MetricAlarm")
+                ? metricsService.describeAlarms(alarmNames, prefix, region) : List.of();

        var xml = new XmlBuilder().start("MetricAlarms");
        for (MetricAlarm a : alarms) {
            toAlarmXml(xml, a);
        }
-        xml.end("MetricAlarms");
+        xml.end("MetricAlarms").start("CompositeAlarms");
+        if (types.contains("CompositeAlarm")) {
+            for (CompositeAlarm alarm : metricsService.describeCompositeAlarms(alarmNames, prefix, region)) {
+                xml.start("member");
+                describeAlarmFields(xml, alarm);
+                xml.elem("AlarmRule", alarm.getAlarmRule()).end("member");
+            }
+        }
+        xml.end("CompositeAlarms").start("LogAlarms").end("LogAlarms");
        return Response.ok(AwsQueryResponse.envelope("DescribeAlarms", null, xml.build())).build();
    }

@@ -590,42 +636,63 @@ public class CloudWatchMetricsQueryHandler {
    // ──────────────────────────── Parsing Helpers ────────────────────────────

    private List<MetricDatum> parseMetricData(MultivaluedMap<String, String> params) {
-        LOG.infov("Query PutMetricData params: {0}", params);
+        List<MetricDatum> datums = parseMetricData(params, "MetricData");
+        // An empty EntityMetricData entry serializes to no keys, so its index is absent
+        // while later entries keep theirs: iterate the indexes present, not 1..first gap.
+        SortedSet<Integer> entityIndexes = new TreeSet<>();
+        for (String key : params.keySet()) {
+            Matcher matcher = ENTITY_METRIC_DATA_MEMBER.matcher(key);
+            if (matcher.lookingAt()) {
+                entityIndexes.add(Integer.parseInt(matcher.group(1)));
+            }
+        }
+        for (int index : entityIndexes) {
+            datums.addAll(parseMetricData(params, "EntityMetricData.member." + index + ".MetricData"));
+        }
+        LOG.debugv("Query PutMetricData parsed {0} datums", datums.size());
+        return datums;
+    }
+
+    private List<MetricDatum> parseMetricData(MultivaluedMap<String, String> params, String listPrefix) {
        List<MetricDatum> datums = new ArrayList<>();
        for (int i = 1; ; i++) {
-            String metricName = params.getFirst("MetricData.member." + i + ".MetricName");
-            if (metricName == null) {
-                break;
+            String memberPrefix = listPrefix + ".member." + i + ".";
+            String metricName = params.getFirst(memberPrefix + "MetricName");
+            if (metricName == null || metricName.isEmpty()) {
+                if (metricName == null && params.keySet().stream().noneMatch(key -> key.startsWith(memberPrefix))) {
+                    break;
+                }
+                throw CloudWatchMetricsException.missingParameter(memberPrefix + "MetricName");
            }
            MetricDatum datum = new MetricDatum();
            datum.setMetricName(metricName);
-            datum.setUnit(params.getFirst("MetricData.member." + i + ".Unit"));
+            datum.setUnit(params.getFirst(listPrefix + ".member." + i + ".Unit"));

-            String valueStr = params.getFirst("MetricData.member." + i + ".Value");
+            String valueStr = params.getFirst(listPrefix + ".member." + i + ".Value");
            if (valueStr != null) {
                datum.setValue(parseDouble(valueStr, 0));
            }

-            String tsStr = params.getFirst("MetricData.member." + i + ".Timestamp");
+            String tsStr = params.getFirst(listPrefix + ".member." + i + ".Timestamp");
            if (tsStr != null) {
                Instant ts = parseInstant(tsStr);
                datum.setTimestamp(ts != null ? ts.getEpochSecond() : 0);
            }

            // StatisticValues
-            String sc = params.getFirst("MetricData.member." + i + ".StatisticValues.SampleCount");
+            String sc = params.getFirst(listPrefix + ".member." + i + ".StatisticValues.SampleCount");
            if (sc != null) {
                datum.setSampleCount(parseDouble(sc, 0));
-                datum.setSum(parseDouble(params.getFirst("MetricData.member." + i + ".StatisticValues.Sum"), 0));
-                datum.setMinimum(parseDouble(params.getFirst("MetricData.member." + i + ".StatisticValues.Minimum"), 0));
-                datum.setMaximum(parseDouble(params.getFirst("MetricData.member." + i + ".StatisticValues.Maximum"), 0));
+                datum.setSum(parseDouble(params.getFirst(listPrefix + ".member." + i + ".StatisticValues.Sum"), 0));
+                datum.setMinimum(parseDouble(params.getFirst(listPrefix + ".member." + i + ".StatisticValues.Minimum"), 0));
+                datum.setMaximum(parseDouble(params.getFirst(listPrefix + ".member." + i + ".StatisticValues.Maximum"), 0));
            }

            // Dimensions
            List<Dimension> dims = new ArrayList<>();
            for (int j = 1; ; j++) {
-                String dimName = params.getFirst("MetricData.member." + i + ".Dimensions.member." + j + ".Name");
-                String dimValue = params.getFirst("MetricData.member." + i + ".Dimensions.member." + j + ".Value");
+                String dimName = params.getFirst(listPrefix + ".member." + i + ".Dimensions.member." + j + ".Name");
+                String dimValue = params.getFirst(listPrefix + ".member." + i + ".Dimensions.member." + j + ".Value");
                if (dimName == null) {
                    break;
                }
@@ -653,14 +720,12 @@ public class CloudWatchMetricsQueryHandler {

    private MetricAlarm parseAlarm(MultivaluedMap<String, String> params) {
        MetricAlarm a = new MetricAlarm();
-        a.setAlarmName(params.getFirst("AlarmName"));
-        a.setAlarmDescription(params.getFirst("AlarmDescription"));
-        String actionsEnabled = params.getFirst("ActionsEnabled");
-        a.setActionsEnabled(actionsEnabled == null || Boolean.parseBoolean(actionsEnabled));
+        parseAlarmFields(params, a);
        a.setMetricName(params.getFirst("MetricName"));
        a.setNamespace(params.getFirst("Namespace"));
        a.setStatistic(params.getFirst("Statistic"));
-        a.setPeriod(parseIntParam(params, "Period", 60));
+        a.setMetrics(parseAlarmMetricQueries(params));
+        a.setPeriod(a.getMetrics().isEmpty() ? parseIntParam(params, "Period", 60) : null);
        a.setUnit(params.getFirst("Unit"));
        a.setEvaluationPeriods(parseIntParam(params, "EvaluationPeriods", 1));
        String datapointsToAlarm = params.getFirst("DatapointsToAlarm");
@@ -680,38 +745,100 @@ public class CloudWatchMetricsQueryHandler {
        }
        a.setDimensions(dims);

-        // Actions
-        for (int i = 1; ; i++) {
-            String act = params.getFirst("OKActions.member." + i);
-            if (act == null) break;
-            a.getOkActions().add(act);
-        }
-        for (int i = 1; ; i++) {
-            String act = params.getFirst("AlarmActions.member." + i);
-            if (act == null) break;
-            a.getAlarmActions().add(act);
-        }
-        for (int i = 1; ; i++) {
-            String act = params.getFirst("InsufficientDataActions.member." + i);
-            if (act == null) break;
-            a.getInsufficientDataActions().add(act);
-        }
-
-        // Tags
-        Map<String, String> tags = new LinkedHashMap<>();
-        for (int i = 1; ; i++) {
-            String key = params.getFirst("Tags.member." + i + ".Key");
-            if (key == null) break;
-            tags.put(key, params.getFirst("Tags.member." + i + ".Value"));
-        }
-        a.setTags(tags);
-
        return a;
    }

+    private void parseAlarmFields(MultivaluedMap<String, String> params, Alarm alarm) {
+        alarm.setAlarmName(params.getFirst("AlarmName"));
+        alarm.setAlarmDescription(params.getFirst("AlarmDescription"));
+        String actionsEnabled = params.getFirst("ActionsEnabled");
+        alarm.setActionsEnabled(actionsEnabled == null || Boolean.parseBoolean(actionsEnabled));
+        alarm.setAlarmActions(alarmMembers(params, "AlarmActions"));
+        alarm.setOkActions(alarmMembers(params, "OKActions"));
+        alarm.setInsufficientDataActions(alarmMembers(params, "InsufficientDataActions"));
+        Map<String, String> tags = new LinkedHashMap<>();
+        for (int i = 1; params.getFirst("Tags.member." + i + ".Key") != null; i++) {
+            tags.put(params.getFirst("Tags.member." + i + ".Key"), params.getFirst("Tags.member." + i + ".Value"));
+        }
+        alarm.setTags(tags);
+    }
+
+    private List<AlarmMetricDataQuery> parseAlarmMetricQueries(MultivaluedMap<String, String> params) {
+        List<AlarmMetricDataQuery> queries = new ArrayList<>();
+        for (int index = 1; ; index++) {
+            String prefix = "Metrics.member." + index;
+            String id = params.getFirst(prefix + ".Id");
+            if (id == null) {
+                break;
+            }
+            AlarmMetricDataQuery.MetricStat metricStat = null;
+            String metricPrefix = prefix + ".MetricStat.Metric";
+            if (params.getFirst(metricPrefix + ".Namespace") != null) {
+                List<AlarmMetricDataQuery.MetricDimension> dimensions = null;
+                for (int dimensionIndex = 1; ; dimensionIndex++) {
+                    String dimensionPrefix = metricPrefix + ".Dimensions.member." + dimensionIndex;
+                    String name = params.getFirst(dimensionPrefix + ".Name");
+                    if (name == null) {
+                        break;
+                    }
+                    if (dimensions == null) {
+                        dimensions = new ArrayList<>();
+                    }
+                    dimensions.add(new AlarmMetricDataQuery.MetricDimension(
+                            name, params.getFirst(dimensionPrefix + ".Value")));
+                }
+                AlarmMetricDataQuery.Metric metric = new AlarmMetricDataQuery.Metric(
+                        params.getFirst(metricPrefix + ".Namespace"),
+                        params.getFirst(metricPrefix + ".MetricName"), dimensions);
+                metricStat = new AlarmMetricDataQuery.MetricStat(metric,
+                        optionalInteger(params.getFirst(prefix + ".MetricStat.Period")),
+                        params.getFirst(prefix + ".MetricStat.Stat"), params.getFirst(prefix + ".MetricStat.Unit"));
+            }
+            String returnData = params.getFirst(prefix + ".ReturnData");
+            queries.add(new AlarmMetricDataQuery(id, params.getFirst(prefix + ".Expression"),
+                    params.getFirst(prefix + ".Label"), returnData == null ? null : Boolean.valueOf(returnData),
+                    optionalInteger(params.getFirst(prefix + ".Period")),
+                    params.getFirst(prefix + ".AccountId"), metricStat));
+        }
+        return queries;
+    }
+
+    private static Integer optionalInteger(String value) {
+        return value == null ? null : Integer.valueOf(value);
+    }
+
    private void toAlarmXml(XmlBuilder xml, MetricAlarm a) {
-        xml.start("member")
-                .elem("AlarmName", a.getAlarmName())
+        xml.start("member");
+        describeAlarmFields(xml, a);
+        if (!a.getMetrics().isEmpty()) {
+            toAlarmMetricsXml(xml, a.getMetrics());
+        } else {
+            xml.start("Dimensions");
+            for (Dimension d : a.getDimensions()) {
+                xml.start("member").elem("Name", d.name()).elem("Value", d.value()).end("member");
+            }
+            xml.end("Dimensions")
+                    .elem("MetricName", a.getMetricName())
+                    .elem("Namespace", a.getNamespace())
+                    .elem("Statistic", a.getStatistic())
+                    .elem("Period", a.getPeriod() == null ? null : a.getPeriod().toString())
+                    .elem("Unit", a.getUnit());
+        }
+
+        xml.elem("EvaluationPeriods", String.valueOf(a.getEvaluationPeriods()))
+                .elem("Threshold", String.valueOf(a.getThreshold()))
+                .elem("ComparisonOperator", a.getComparisonOperator())
+                .elem("TreatMissingData", a.getTreatMissingData());
+        // Only an alarm the caller gave an M for carries the member, matching what AWS returns.
+        if (a.getDatapointsToAlarm() != null) {
+            xml.elem("DatapointsToAlarm", String.valueOf(a.getDatapointsToAlarm()));
+        }
+
+        xml.end("member");
+    }
+
+    private void describeAlarmFields(XmlBuilder xml, Alarm a) {
+        xml.elem("AlarmName", a.getAlarmName())
                .elem("AlarmArn", a.getAlarmArn())
                .elem("AlarmDescription", a.getAlarmDescription());
        xml.start("AlarmActions");
@@ -726,31 +853,41 @@ public class CloudWatchMetricsQueryHandler {
        xml.start("InsufficientDataActions");
        a.getInsufficientDataActions().forEach(act -> xml.elem("member", act));
        xml.end("InsufficientDataActions");
-        xml.start("Dimensions");
-        for (Dimension d : a.getDimensions()) {
-            xml.start("member").elem("Name", d.name()).elem("Value", d.value()).end("member");
-        }
-        xml.end("Dimensions");
-
        xml.elem("StateValue", a.getStateValue())
                .elem("StateReason", a.getStateReason())
                .elem("StateReasonData", a.getStateReasonData())
-                .elem("StateUpdatedTimestamp", Instant.ofEpochSecond(a.getStateUpdatedTimestamp()).toString())
-                .elem("MetricName", a.getMetricName())
-                .elem("Namespace", a.getNamespace())
-                .elem("Statistic", a.getStatistic())
-                .elem("Period", String.valueOf(a.getPeriod()))
-                .elem("Unit", a.getUnit())
-                .elem("EvaluationPeriods", String.valueOf(a.getEvaluationPeriods()))
-                .elem("Threshold", String.valueOf(a.getThreshold()))
-                .elem("ComparisonOperator", a.getComparisonOperator())
-                .elem("TreatMissingData", a.getTreatMissingData());
-        // Only an alarm the caller gave an M for carries the member, matching what AWS returns.
-        if (a.getDatapointsToAlarm() != null) {
-            xml.elem("DatapointsToAlarm", String.valueOf(a.getDatapointsToAlarm()));
-        }
+                .elem("StateUpdatedTimestamp", Instant.ofEpochSecond(a.getStateUpdatedTimestamp()).toString());
+    }

-        xml.end("member");
+    private void toAlarmMetricsXml(XmlBuilder xml, List<AlarmMetricDataQuery> metrics) {
+        xml.start("Metrics");
+        for (AlarmMetricDataQuery query : metrics) {
+            xml.start("member").elem("Id", query.id()).elem("Expression", query.expression())
+                    .elem("Label", query.label()).elem("AccountId", query.accountId())
+                    .elem("Period", query.period() == null ? null : query.period().toString())
+                    .elem("ReturnData", query.returnData() == null ? null : query.returnData().toString());
+            AlarmMetricDataQuery.MetricStat stat = query.metricStat();
+            if (stat != null) {
+                xml.start("MetricStat");
+                AlarmMetricDataQuery.Metric metric = stat.metric();
+                if (metric != null) {
+                    xml.start("Metric").elem("Namespace", metric.namespace()).elem("MetricName", metric.metricName());
+                    if (metric.dimensions() != null) {
+                        xml.start("Dimensions");
+                        for (AlarmMetricDataQuery.MetricDimension dimension : metric.dimensions()) {
+                            xml.start("member").elem("Name", dimension.name()).elem("Value", dimension.value())
+                                    .end("member");
+                        }
+                        xml.end("Dimensions");
+                    }
+                    xml.end("Metric");
+                }
+                xml.elem("Period", stat.period() == null ? null : stat.period().toString())
+                        .elem("Stat", stat.stat()).elem("Unit", stat.unit()).end("MetricStat");
+            }
+            xml.end("member");
+        }
+        xml.end("Metrics");
    }

    private Instant parseInstant(String value) {
@@ -1,10 +1,15 @@
 package io.github.hectorvent.floci.services.cloudwatch.metrics;

+import com.fasterxml.jackson.core.type.TypeReference;
+import io.github.hectorvent.floci.core.common.AwsArnUtils;
 import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.core.common.RegionResolver;
+import io.github.hectorvent.floci.core.common.SmithyValidationErrors;
 import io.github.hectorvent.floci.core.storage.AccountAwareStorageBackend;
 import io.github.hectorvent.floci.core.storage.StorageBackend;
 import io.github.hectorvent.floci.core.storage.StorageFactory;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Dimension;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
@@ -14,11 +19,16 @@ import jakarta.inject.Inject;
 import org.jboss.logging.Logger;

 import java.time.Instant;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 import java.util.stream.Collectors;

@@ -27,25 +37,41 @@ public class CloudWatchMetricsService {

    private static final Logger LOG = Logger.getLogger(CloudWatchMetricsService.class);

+    private static final List<String> ALARM_TYPES = List.of("CompositeAlarm", "MetricAlarm", "LogAlarm");
+
    private final StorageBackend<String, MetricDatum> metricStore;
-    private final StorageBackend<String, MetricAlarm> alarmStore;
+    private final StorageBackend<String, Alarm> alarmStore;
    private final RegionResolver regionResolver;
+    private final AlarmSnsNotifier alarmSnsNotifier;
+
+    public CloudWatchMetricsService(StorageFactory storageFactory, RegionResolver regionResolver) {
+        this(storageFactory, regionResolver, null);
+    }

    @Inject
-    public CloudWatchMetricsService(StorageFactory storageFactory, RegionResolver regionResolver) {
+    public CloudWatchMetricsService(StorageFactory storageFactory, RegionResolver regionResolver,
+                                    AlarmSnsNotifier alarmSnsNotifier) {
        this.metricStore = storageFactory.create("cloudwatchmetrics", "cwmetrics.json",
                new TypeReference<Map<String, MetricDatum>>() {});
        this.alarmStore = storageFactory.create("cloudwatchmetrics", "cwalarms.json",
-                new TypeReference<Map<String, MetricAlarm>>() {});
+                new TypeReference<Map<String, Alarm>>() {});
        this.regionResolver = regionResolver;
+        this.alarmSnsNotifier = alarmSnsNotifier;
    }

    CloudWatchMetricsService(StorageBackend<String, MetricDatum> metricStore,
-                             StorageBackend<String, MetricAlarm> alarmStore,
+                             StorageBackend<String, Alarm> alarmStore,
                             RegionResolver regionResolver) {
+        this(metricStore, alarmStore, regionResolver, null);
+    }
+
+    CloudWatchMetricsService(StorageBackend<String, MetricDatum> metricStore,
+                             StorageBackend<String, Alarm> alarmStore,
+                             RegionResolver regionResolver, AlarmSnsNotifier alarmSnsNotifier) {
        this.metricStore = metricStore;
        this.alarmStore = alarmStore;
        this.regionResolver = regionResolver;
+        this.alarmSnsNotifier = alarmSnsNotifier;
    }

    public void putMetricData(String namespace, List<MetricDatum> datums, String region) {
@@ -282,85 +308,293 @@ public class CloudWatchMetricsService {
        };
    }

-    public void putMetricAlarm(MetricAlarm alarm, String region) {
+    public synchronized void putMetricAlarm(MetricAlarm alarm, String region) {
+        putAlarm(alarm, region);
+        evaluateComposites(region, Set.of(alarm.getAlarmName()), null);
+    }
+
+    public void putCompositeAlarm(CompositeAlarm alarm, String region) {
+        putCompositeAlarm(alarm, region, true);
+    }
+
+    public synchronized void putCompositeAlarm(CompositeAlarm alarm, String region, boolean replaceExisting) {
+        if (!replaceExisting && alarmStore.get(region + "::" + alarm.getAlarmName()).isPresent()) {
+            throw new AwsException("AlreadyExists", "Alarm already exists: " + alarm.getAlarmName(), 400);
+        }
+        Set<String> references = alarmReferences(alarm, region);
+        if (references.size() > 100) {
+            throw new AwsException("LimitExceeded", "AlarmRule references more than 100 child alarms", 400);
+        }
+        List<CompositeAlarm> existing = describeCompositeAlarms(null, null, region);
+        for (String reference : references) {
+            long parents = existing.stream().filter(parent -> !parent.getAlarmName().equals(alarm.getAlarmName()))
+                    .filter(parent -> alarmReferences(parent, region).contains(reference))
+                    .count();
+            if (parents >= 150) {
+                throw new AwsException("LimitExceeded", "An alarm can be referenced by at most 150 composite alarms", 400);
+            }
+        }
+        boolean created = alarmStore.get(region + "::" + alarm.getAlarmName()).isEmpty();
+        putAlarm(alarm, region);
+        if (created) {
+            evaluateComposites(region, Set.of(), alarm.getAlarmName());
+        }
+    }
+
+    private Set<String> alarmReferences(CompositeAlarm alarm, String region) {
+        return CompositeAlarmRule.parse(alarm.getAlarmRule()).references().stream()
+                .map(reference -> AwsArnUtils.isArn(reference) ? reference
+                        : regionResolver.buildArn("cloudwatch", region, "alarm:" + reference))
+                .collect(Collectors.toSet());
+    }
+
+    private void putAlarm(Alarm alarm, String region) {
+        String name = alarm.getAlarmName();
+        if (name == null || name.isBlank() || name.length() > 255) {
+            throw SmithyValidationErrors.validationError(name == null ? SmithyValidationErrors.notNull("alarmName")
+                    : "Value '" + name + "' at 'alarmName' failed to satisfy constraint: Member must have length "
+                            + (name.length() > 255 ? "less than or equal to 255" : "greater than or equal to 1"));
+        }
+        Alarm previous = alarmStore.get(region + "::" + name).orElse(null);
+        if (previous != null) {
+            if (!previous.getClass().equals(alarm.getClass())) {
+                throw new AwsException("ValidationError", "An alarm of another type already has this name", 400);
+            }
+            if (alarm instanceof CompositeAlarm) {
+                alarm.setStateValue(previous.getStateValue());
+                alarm.setStateReason(previous.getStateReason());
+                alarm.setStateReasonData(previous.getStateReasonData());
+                alarm.setStateUpdatedTimestamp(previous.getStateUpdatedTimestamp());
+                alarm.setTags(new HashMap<>(previous.getTags()));
+            }
+        }
        if (alarm.getAlarmArn() == null) {
-            alarm.setAlarmArn(regionResolver.buildArn("cloudwatch", region, "alarm:" + alarm.getAlarmName()));
+            alarm.setAlarmArn(regionResolver.buildArn("cloudwatch", region, "alarm:" + name));
        }
        alarm.setRegion(region);
        alarm.setAlarmConfigurationUpdatedTimestamp(Instant.now().getEpochSecond());
-        alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
-        LOG.infov("PutMetricAlarm: {0} in {1}", alarm.getAlarmName(), region);
+        alarmStore.put(region + "::" + name, alarm);
+        LOG.infov("Put {0}: {1} in {2}", alarm.getClass().getSimpleName(), name, region);
    }

-    /** Every stored alarm, across all regions. Used by the background {@link AlarmEvaluator}
-     * tick, which has no per-request region to scope a lookup to. */
+    /** Metric alarms evaluated by the existing metric evaluator. */
    public List<MetricAlarm> allAlarms() {
-        return alarmStore.scan(k -> true);
+        return alarmStore.scan(k -> true).stream().filter(MetricAlarm.class::isInstance)
+                .map(MetricAlarm.class::cast).toList();
    }

-    public List<MetricAlarm> describeAlarms(List<String> alarmNames, String alarmNamePrefix, String region) {
-        String prefix = region + "::";
-        List<MetricAlarm> all = alarmStore.scan(k -> k.startsWith(prefix));
-
-        if (alarmNames != null && !alarmNames.isEmpty()) {
-            return all.stream().filter(a -> alarmNames.contains(a.getAlarmName())).toList();
-        }
-        if (alarmNamePrefix != null && !alarmNamePrefix.isBlank()) {
-            return all.stream().filter(a -> a.getAlarmName().startsWith(alarmNamePrefix)).toList();
-        }
-        return all;
+    public List<MetricAlarm> describeAlarms(List<String> names, String prefix, String region) {
+        return matchingAlarms(names, prefix, region).stream().filter(MetricAlarm.class::isInstance)
+                .map(MetricAlarm.class::cast).toList();
    }

-    public void deleteAlarms(List<String> alarmNames, String region) {
+    public void validateAlarmTypes(List<String> types) {
+        if (!ALARM_TYPES.containsAll(types)) {
+            throw SmithyValidationErrors.validationError(
+                    SmithyValidationErrors.notAllInEnum(types, "alarmTypes", ALARM_TYPES));
+        }
+    }
+
+    public List<CompositeAlarm> describeCompositeAlarms(List<String> names, String prefix, String region) {
+        return matchingAlarms(names, prefix, region).stream().filter(CompositeAlarm.class::isInstance)
+                .map(CompositeAlarm.class::cast).toList();
+    }
+
+    private List<Alarm> matchingAlarms(List<String> names, String prefix, String region) {
+        return alarmStore.scan(k -> k.startsWith(region + "::")).stream()
+                .filter(a -> names == null || names.isEmpty() || names.contains(a.getAlarmName()))
+                .filter(a -> prefix == null || a.getAlarmName().startsWith(prefix)).toList();
+    }
+
+    private Map<String, Alarm> alarmIndex(String region) {
+        Map<String, Alarm> alarms = new HashMap<>();
+        for (Alarm alarm : alarmStore.scan(k -> k.startsWith(region + "::"))) {
+            alarms.put(alarm.getAlarmName(), alarm);
+            alarms.put(alarm.getAlarmArn(), alarm);
+        }
+        return alarms;
+    }
+
+    private void evaluateComposites(String region, Set<String> changedAlarmNames, String newAlarm) {
+        if (changedAlarmNames.isEmpty() && newAlarm == null) {
+            return;
+        }
+        Map<String, Alarm> alarms = alarmIndex(region);
+        Set<String> changed = new HashSet<>(changedAlarmNames);
+        for (String name : changedAlarmNames) {
+            changed.add(regionResolver.buildArn("cloudwatch", region, "alarm:" + name));
+        }
+        Map<String, CompositeAlarmRule.Rule> candidates = new HashMap<>();
+        for (Alarm alarm : new HashSet<>(alarms.values())) {
+            if (alarm instanceof CompositeAlarm composite && !changedAlarmNames.contains(alarm.getAlarmName())) {
+                candidates.put(alarm.getAlarmName(), CompositeAlarmRule.parse(composite.getAlarmRule()));
+            }
+        }
+        Set<String> affected = new HashSet<>(changed);
+        Map<String, CompositeAlarmRule.Rule> pending = new HashMap<>();
+        boolean discovered;
+        do {
+            discovered = false;
+            Iterator<Map.Entry<String, CompositeAlarmRule.Rule>> iterator = candidates.entrySet().iterator();
+            while (iterator.hasNext()) {
+                Map.Entry<String, CompositeAlarmRule.Rule> next = iterator.next();
+                if (next.getKey().equals(newAlarm) || next.getValue().references().stream().anyMatch(affected::contains)) {
+                    pending.put(next.getKey(), next.getValue());
+                    affected.add(next.getKey());
+                    affected.add(alarms.get(next.getKey()).getAlarmArn());
+                    iterator.remove();
+                    discovered = true;
+                }
+            }
+        } while (discovered);
+        Set<String> cycles = pending.keySet().stream()
+                .filter(name -> isCyclic(name, alarms)).collect(Collectors.toSet());
+        boolean progress;
+        do {
+            progress = false;
+            Iterator<Map.Entry<String, CompositeAlarmRule.Rule>> iterator = pending.entrySet().iterator();
+            while (iterator.hasNext()) {
+                Map.Entry<String, CompositeAlarmRule.Rule> next = iterator.next();
+                boolean blocked = next.getValue().references().stream().map(alarms::get)
+                        .anyMatch(child -> child != null && pending.containsKey(child.getAlarmName()));
+                if (blocked || cycles.contains(next.getKey())) {
+                    continue;
+                }
+                if (!next.getKey().equals(newAlarm)
+                        && next.getValue().references().stream().noneMatch(changed::contains)) {
+                    iterator.remove();
+                    progress = true;
+                    continue;
+                }
+                Alarm alarm = alarms.get(next.getKey());
+                boolean triggered = next.getValue().evaluate(reference -> {
+                    Alarm child = alarms.get(reference);
+                    return child == null ? null : child.getStateValue();
+                });
+                String state = triggered ? "ALARM" : "OK";
+                if (!state.equals(alarm.getStateValue())) {
+                    alarm.setStateValue(state);
+                    alarm.setStateReason("AlarmRule evaluated to " + state);
+                    alarm.setStateReasonData(null);
+                    alarm.setStateUpdatedTimestamp(Instant.now().getEpochSecond());
+                    alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
+                    changed.add(alarm.getAlarmName());
+                    changed.add(alarm.getAlarmArn());
+                }
+                iterator.remove();
+                progress = true;
+            }
+        } while (progress && !pending.isEmpty());
+        if (!pending.isEmpty()) {
+            LOG.debugv("Composite alarm evaluation stopped at cyclic dependencies: {0}", pending.keySet());
+        }
+    }
+
+    public synchronized void deleteAlarms(List<String> alarmNames, String region) {
+        Map<String, Alarm> alarms = alarmIndex(region);
+        long composites = alarmNames.stream().map(alarms::get).filter(CompositeAlarm.class::isInstance).count();
+        if (composites > 1) {
+            throw new AwsException("ValidationError", "DeleteAlarms accepts at most one composite alarm", 400);
+        }
        for (String name : alarmNames) {
+            if (isCyclic(name, alarms)) {
+                throw new AwsException("ValidationError", "Break the composite alarm cycle before deleting " + name, 400);
+            }
+        }
+        Set<String> deletedNames = new HashSet<>();
+        for (String name : alarmNames) {
+            if (alarmStore.get(region + "::" + name).isPresent()) {
+                deletedNames.add(name);
+            }
            alarmStore.delete(region + "::" + name);
        }
+        evaluateComposites(region, deletedNames, null);
        LOG.infov("Deleted alarms: {0} in {1}", alarmNames, region);
    }

-    public void setAlarmState(String alarmName, String stateValue, String stateReason, String stateReasonData, String region) {
-        String key = region + "::" + alarmName;
-        MetricAlarm alarm = alarmStore.get(key)
-                .orElseThrow(() -> new AwsException("ResourceNotFound", "Alarm not found: " + alarmName, 404));
-
-        alarm.setStateValue(stateValue);
-        alarm.setStateReason(stateReason);
-        alarm.setStateReasonData(stateReasonData);
-        alarm.setStateUpdatedTimestamp(Instant.now().getEpochSecond());
-
-        alarmStore.put(key, alarm);
-        LOG.infov("SetAlarmState: {0} -> {1}", alarmName, stateValue);
+    private boolean isCyclic(String name, Map<String, Alarm> alarms) {
+        Set<String> visited = new HashSet<>();
+        ArrayDeque<String> pending = new ArrayDeque<>();
+        pending.add(name);
+        while (!pending.isEmpty()) {
+            Alarm next = alarms.get(pending.remove());
+            if (next instanceof CompositeAlarm composite && visited.add(next.getAlarmName())) {
+                for (String reference : CompositeAlarmRule.parse(composite.getAlarmRule()).references()) {
+                    Alarm child = alarms.get(reference);
+                    if (child != null && child.getAlarmName().equals(name)) {
+                        return true;
+                    }
+                    if (child != null) {
+                        pending.add(child.getAlarmName());
+                    }
+                }
+            }
+        }
+        return false;
    }

-    public Map<String, String> listTagsForResource(String resourceArn, String region) {
+    public void setAlarmState(String alarmName, String stateValue, String stateReason, String stateReasonData, String region) {
+        List<AlarmSnsNotifier.Notification> notifications = List.of();
+        synchronized (this) {
+            String key = region + "::" + alarmName;
+            Alarm alarm = alarmStore.get(key)
+                    .orElseThrow(() -> new AwsException("ResourceNotFound", "Alarm not found: " + alarmName, 404));
+
+            String oldState = alarm.getStateValue();
+            alarm.setStateValue(stateValue);
+            alarm.setStateReason(stateReason);
+            alarm.setStateReasonData(stateReasonData);
+            alarm.setStateUpdatedTimestamp(Instant.now().getEpochSecond());
+
+            alarmStore.put(key, alarm);
+            evaluateComposites(region, Set.of(alarmName), null);
+            LOG.infov("SetAlarmState: {0} -> {1}", alarmName, stateValue);
+            if (alarmSnsNotifier != null && alarm instanceof MetricAlarm metricAlarm) {
+                notifications = alarmSnsNotifier.prepareTransition(metricAlarm, oldState);
+            }
+        }
+        if (alarmSnsNotifier != null) {
+            alarmSnsNotifier.publish(notifications);
+        }
+    }
+
+    /**
+     * Resolves the alarm an ARN names, or reports that nothing does.
+     *
+     * <p>CloudWatch's three tag operations each declare {@code ResourceNotFoundException},
+     * which is a different shape from the {@code ResourceNotFound} that {@code SetAlarmState}
+     * and {@code GetDashboard} declare; the SDK maps the two codes to two exception classes,
+     * so the tag path uses the longer one rather than the code used elsewhere in this service.
+     *
+     * <p>The message names the ARN rather than asserting it was an alarm, because both tag
+     * handlers route every ARN that is not a dashboard and not a metric stream here. That
+     * includes kinds AWS considers taggable and Floci does not serve, a Contributor Insights
+     * {@code insight-rule/} ARN being the one AWS documents; reporting that no resource
+     * matches the ARN is true of those, where "alarm not found" would not be.
+     */
+    private Alarm requireAlarm(String resourceArn, String region) {
        return alarmStore.scan(k -> k.startsWith(region + "::"))
                .stream()
-                .filter(a -> resourceArn.equals(a.getAlarmArn()))
+                .filter(a -> a.getAlarmArn() != null && a.getAlarmArn().equals(resourceArn))
                .findFirst()
-                .map(MetricAlarm::getTags)
-                .orElse(Map.of());
+                .orElseThrow(() -> new AwsException("ResourceNotFoundException",
+                        "No CloudWatch resource matches the ARN " + resourceArn + ".", 404));
    }

-    public void tagResource(String resourceArn, Map<String, String> tags, String region) {
-        alarmStore.scan(k -> k.startsWith(region + "::"))
-                .stream()
-                .filter(a -> resourceArn.equals(a.getAlarmArn()))
-                .findFirst()
-                .ifPresent(alarm -> {
-                    alarm.getTags().putAll(tags);
-                    alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
-                });
+    public synchronized Map<String, String> listTagsForResource(String resourceArn, String region) {
+        return new HashMap<>(requireAlarm(resourceArn, region).getTags());
    }

-    public void untagResource(String resourceArn, List<String> tagKeys, String region) {
-        alarmStore.scan(k -> k.startsWith(region + "::"))
-                .stream()
-                .filter(a -> resourceArn.equals(a.getAlarmArn()))
-                .findFirst()
-                .ifPresent(alarm -> {
-                    tagKeys.forEach(alarm.getTags()::remove);
-                    alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
-                });
+    public synchronized void tagResource(String resourceArn, Map<String, String> tags, String region) {
+        Alarm alarm = requireAlarm(resourceArn, region);
+        alarm.getTags().putAll(tags);
+        alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
+    }
+
+    public synchronized void untagResource(String resourceArn, List<String> tagKeys, String region) {
+        Alarm alarm = requireAlarm(resourceArn, region);
+        tagKeys.forEach(alarm.getTags()::remove);
+        alarmStore.put(region + "::" + alarm.getAlarmName(), alarm);
    }

    // ──────────────────────────── Helpers ────────────────────────────
@@ -0,0 +1,184 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import io.github.hectorvent.floci.core.common.AwsException;
+import io.github.hectorvent.floci.core.common.SmithyValidationErrors;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Function;
+
+/** CloudWatch's boolean alarm language, parsed completely before any alarm is stored. */
+final class CompositeAlarmRule {
+    private final String input;
+    private final Set<String> references = new HashSet<>();
+    private int offset;
+    private int elements;
+
+    private CompositeAlarmRule(String input) {
+        this.input = input;
+    }
+
+    static Rule parse(String input) {
+        if (input == null || input.isBlank() || input.length() > 10240) {
+            throw SmithyValidationErrors.validationError(input == null ? SmithyValidationErrors.notNull("alarmRule")
+                    : "Value '" + input + "' at 'alarmRule' failed to satisfy constraint: Member must have length "
+                            + (input.length() > 10240 ? "less than or equal to 10240" : "greater than or equal to 1"));
+        }
+        CompositeAlarmRule parser = new CompositeAlarmRule(input);
+        Expression expression = parser.or();
+        parser.whitespace();
+        if (parser.offset != input.length()) {
+            throw invalid("Invalid AlarmRule");
+        }
+        return new Rule(expression, Set.copyOf(parser.references));
+    }
+
+    private Expression or() {
+        Expression left = and();
+        while (word("OR")) {
+            Expression prior = left;
+            Expression right = and();
+            left = states -> prior.evaluate(states) || right.evaluate(states);
+        }
+        return left;
+    }
+
+    private Expression and() {
+        Expression left = atom();
+        while (word("AND")) {
+            Expression prior = left;
+            Expression right = atom();
+            left = states -> prior.evaluate(states) && right.evaluate(states);
+        }
+        return left;
+    }
+
+    private Expression atom() {
+        boolean negate = false;
+        while (word("NOT")) {
+            negate = !negate;
+        }
+        Expression operand = primary();
+        return negate ? states -> !operand.evaluate(states) : operand;
+    }
+
+    private Expression primary() {
+        element();
+        if (character('(')) {
+            Expression nested = or();
+            require(')');
+            element();
+            return nested;
+        }
+        if (word("TRUE")) {
+            return states -> true;
+        }
+        if (word("FALSE")) {
+            return states -> false;
+        }
+        String state;
+        if (word("ALARM")) {
+            state = "ALARM";
+        } else if (word("OK")) {
+            state = "OK";
+        } else if (word("INSUFFICIENT_DATA")) {
+            state = "INSUFFICIENT_DATA";
+        } else {
+            throw invalid("Expected an alarm state, boolean, NOT, or parenthesis");
+        }
+        require('(');
+        whitespace();
+        String name;
+        if (character('"')) {
+            StringBuilder quoted = new StringBuilder();
+            boolean closed = false;
+            while (offset < input.length()) {
+                char next = input.charAt(offset++);
+                if (next == '"') {
+                    closed = true;
+                    break;
+                }
+                if (next == '\\') {
+                    if (offset == input.length()) {
+                        throw invalid("Unterminated quoted alarm name");
+                    }
+                    next = input.charAt(offset++);
+                    if (next != '\\' && next != '"') {
+                        throw invalid("Invalid quoted alarm name escape");
+                    }
+                }
+                quoted.append(next);
+            }
+            if (!closed) {
+                throw invalid("Unterminated quoted alarm name");
+            }
+            name = quoted.toString();
+        } else {
+            int start = offset;
+            while (offset < input.length() && input.charAt(offset) != ')') {
+                offset++;
+            }
+            name = input.substring(start, offset).trim();
+        }
+        if (name.isEmpty()) {
+            throw invalid("An alarm name or ARN is required");
+        }
+        require(')');
+        references.add(name);
+        return states -> state.equals(states.apply(name));
+    }
+
+    private void element() {
+        if (++elements > 500) {
+            throw invalid("AlarmRule exceeds 500 child alarms, booleans, and parentheses");
+        }
+    }
+
+    private boolean word(String word) {
+        whitespace();
+        if (!input.startsWith(word, offset)) {
+            return false;
+        }
+        int end = offset + word.length();
+        if (end < input.length() && (Character.isLetterOrDigit(input.charAt(end)) || input.charAt(end) == '_')) {
+            return false;
+        }
+        offset = end;
+        return true;
+    }
+
+    private boolean character(char expected) {
+        whitespace();
+        if (offset < input.length() && input.charAt(offset) == expected) {
+            offset++;
+            return true;
+        }
+        return false;
+    }
+
+    private void require(char expected) {
+        if (!character(expected)) {
+            throw invalid("Expected '" + expected + "' in AlarmRule");
+        }
+    }
+
+    private void whitespace() {
+        while (offset < input.length() && Character.isWhitespace(input.charAt(offset))) {
+            offset++;
+        }
+    }
+
+    private static AwsException invalid(String message) {
+        return new AwsException("ValidationError", message, 400);
+    }
+
+    record Rule(Expression expression, Set<String> references) {
+        boolean evaluate(Function<String, String> states) {
+            return expression.evaluate(states);
+        }
+    }
+
+    interface Expression {
+        boolean evaluate(Function<String, String> states);
+    }
+}
@@ -0,0 +1,87 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics.model;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import io.quarkus.runtime.annotations.RegisterForReflection;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+@RegisterForReflection
+@JsonIgnoreProperties(ignoreUnknown = true)
+@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY,
+        property = "alarmType", defaultImpl = MetricAlarm.class)
+@JsonSubTypes({@JsonSubTypes.Type(value = MetricAlarm.class, name = "MetricAlarm"),
+        @JsonSubTypes.Type(value = CompositeAlarm.class, name = "CompositeAlarm")})
+public abstract class Alarm {
+    private String alarmName;
+    private String alarmArn;
+    private String alarmDescription;
+    private long alarmConfigurationUpdatedTimestamp;
+    private boolean actionsEnabled;
+    private List<String> okActions = new ArrayList<>();
+    private List<String> alarmActions = new ArrayList<>();
+    private List<String> insufficientDataActions = new ArrayList<>();
+    private String stateValue = "INSUFFICIENT_DATA";
+    private String stateReason = "Unchecked";
+    private String stateReasonData;
+    private long stateUpdatedTimestamp;
+    private Map<String, String> tags = new HashMap<>();
+    private String region;
+
+
+    protected Alarm() {
+        long now = Instant.now().getEpochSecond();
+        this.alarmConfigurationUpdatedTimestamp = now;
+        this.stateUpdatedTimestamp = now;
+    }
+
+    public abstract String getAlarmType();
+
+    public String getAlarmName() { return alarmName; }
+    public void setAlarmName(String alarmName) { this.alarmName = alarmName; }
+
+    public String getAlarmArn() { return alarmArn; }
+    public void setAlarmArn(String alarmArn) { this.alarmArn = alarmArn; }
+
+    public String getAlarmDescription() { return alarmDescription; }
+    public void setAlarmDescription(String alarmDescription) { this.alarmDescription = alarmDescription; }
+
+    public long getAlarmConfigurationUpdatedTimestamp() { return alarmConfigurationUpdatedTimestamp; }
+    public void setAlarmConfigurationUpdatedTimestamp(long timestamp) { this.alarmConfigurationUpdatedTimestamp = timestamp; }
+
+    public boolean isActionsEnabled() { return actionsEnabled; }
+    public void setActionsEnabled(boolean actionsEnabled) { this.actionsEnabled = actionsEnabled; }
+
+    public List<String> getOkActions() { return okActions; }
+    public void setOkActions(List<String> okActions) { this.okActions = okActions; }
+
+    public List<String> getAlarmActions() { return alarmActions; }
+    public void setAlarmActions(List<String> alarmActions) { this.alarmActions = alarmActions; }
+
+    public List<String> getInsufficientDataActions() { return insufficientDataActions; }
+    public void setInsufficientDataActions(List<String> insufficientDataActions) { this.insufficientDataActions = insufficientDataActions; }
+
+    public String getStateValue() { return stateValue; }
+    public void setStateValue(String stateValue) { this.stateValue = stateValue; }
+
+    public String getStateReason() { return stateReason; }
+    public void setStateReason(String stateReason) { this.stateReason = stateReason; }
+
+    public String getStateReasonData() { return stateReasonData; }
+    public void setStateReasonData(String stateReasonData) { this.stateReasonData = stateReasonData; }
+
+    public long getStateUpdatedTimestamp() { return stateUpdatedTimestamp; }
+    public void setStateUpdatedTimestamp(long stateUpdatedTimestamp) { this.stateUpdatedTimestamp = stateUpdatedTimestamp; }
+
+    public Map<String, String> getTags() { return tags; }
+    public void setTags(Map<String, String> tags) { this.tags = tags; }
+
+
+    public String getRegion() { return region; }
+    public void setRegion(String region) { this.region = region; }
+}
@@ -0,0 +1,46 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics.model;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import io.quarkus.runtime.annotations.RegisterForReflection;
+
+import java.util.List;
+
+/** The persisted AWS wire shape of a metric-math alarm query, including optional members. */
+@RegisterForReflection
+@JsonIgnoreProperties(ignoreUnknown = true)
+@JsonInclude(JsonInclude.Include.NON_NULL)
+public record AlarmMetricDataQuery(
+        @JsonProperty("Id") String id,
+        @JsonProperty("Expression") String expression,
+        @JsonProperty("Label") String label,
+        @JsonProperty("ReturnData") Boolean returnData,
+        @JsonProperty("Period") Integer period,
+        @JsonProperty("AccountId") String accountId,
+        @JsonProperty("MetricStat") MetricStat metricStat) {
+
+    @RegisterForReflection
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    public record MetricStat(
+            @JsonProperty("Metric") Metric metric,
+            @JsonProperty("Period") Integer period,
+            @JsonProperty("Stat") String stat,
+            @JsonProperty("Unit") String unit) { }
+
+    @RegisterForReflection
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    public record Metric(
+            @JsonProperty("Namespace") String namespace,
+            @JsonProperty("MetricName") String metricName,
+            @JsonProperty("Dimensions") List<MetricDimension> dimensions) { }
+
+    @RegisterForReflection
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    public record MetricDimension(
+            @JsonProperty("Name") String name,
+            @JsonProperty("Value") String value) { }
+}
@@ -0,0 +1,14 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics.model;
+
+import io.quarkus.runtime.annotations.RegisterForReflection;
+
+@RegisterForReflection
+public class CompositeAlarm extends Alarm {
+    private String alarmRule;
+
+    @Override
+    public String getAlarmType() { return "CompositeAlarm"; }
+
+    public String getAlarmRule() { return alarmRule; }
+    public void setAlarmRule(String alarmRule) { this.alarmRule = alarmRule; }
+}
@@ -3,32 +3,22 @@ package io.github.hectorvent.floci.services.cloudwatch.metrics.model;
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import io.quarkus.runtime.annotations.RegisterForReflection;

-import java.time.Instant;
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;

@RegisterForReflection
@JsonIgnoreProperties(ignoreUnknown = true)
-public class MetricAlarm {
-    private String alarmName;
-    private String alarmArn;
-    private String alarmDescription;
-    private long alarmConfigurationUpdatedTimestamp;
-    private boolean actionsEnabled;
-    private List<String> okActions = new ArrayList<>();
-    private List<String> alarmActions = new ArrayList<>();
-    private List<String> insufficientDataActions = new ArrayList<>();
-    private String stateValue = "INSUFFICIENT_DATA";
-    private String stateReason = "Unchecked";
-    private String stateReasonData;
-    private long stateUpdatedTimestamp;
+public class MetricAlarm extends Alarm {
+    @Override
+    public String getAlarmType() { return "MetricAlarm"; }
+
    private String metricName;
    private String namespace;
    private String statistic;
    private List<Dimension> dimensions = new ArrayList<>();
-    private int period;
+    /** Single-metric period; absent for alarms whose periods are defined in Metrics. */
+    private Integer period;
+    private List<AlarmMetricDataQuery> metrics = new ArrayList<>();
    private String unit;
    private int evaluationPeriods;
    /**
@@ -43,50 +33,6 @@ public class MetricAlarm {
    private String comparisonOperator;
    private String treatMissingData = "missing";
    private String evaluateLowSampleCountPercentile;
-    private Map<String, String> tags = new HashMap<>();
-    private String region;
-
-    public MetricAlarm() {
-        long now = Instant.now().getEpochSecond();
-        this.alarmConfigurationUpdatedTimestamp = now;
-        this.stateUpdatedTimestamp = now;
-    }
-
-    public String getAlarmName() { return alarmName; }
-    public void setAlarmName(String alarmName) { this.alarmName = alarmName; }
-
-    public String getAlarmArn() { return alarmArn; }
-    public void setAlarmArn(String alarmArn) { this.alarmArn = alarmArn; }
-
-    public String getAlarmDescription() { return alarmDescription; }
-    public void setAlarmDescription(String alarmDescription) { this.alarmDescription = alarmDescription; }
-
-    public long getAlarmConfigurationUpdatedTimestamp() { return alarmConfigurationUpdatedTimestamp; }
-    public void setAlarmConfigurationUpdatedTimestamp(long timestamp) { this.alarmConfigurationUpdatedTimestamp = timestamp; }
-
-    public boolean isActionsEnabled() { return actionsEnabled; }
-    public void setActionsEnabled(boolean actionsEnabled) { this.actionsEnabled = actionsEnabled; }
-
-    public List<String> getOkActions() { return okActions; }
-    public void setOkActions(List<String> okActions) { this.okActions = okActions; }
-
-    public List<String> getAlarmActions() { return alarmActions; }
-    public void setAlarmActions(List<String> alarmActions) { this.alarmActions = alarmActions; }
-
-    public List<String> getInsufficientDataActions() { return insufficientDataActions; }
-    public void setInsufficientDataActions(List<String> insufficientDataActions) { this.insufficientDataActions = insufficientDataActions; }
-
-    public String getStateValue() { return stateValue; }
-    public void setStateValue(String stateValue) { this.stateValue = stateValue; }
-
-    public String getStateReason() { return stateReason; }
-    public void setStateReason(String stateReason) { this.stateReason = stateReason; }
-
-    public String getStateReasonData() { return stateReasonData; }
-    public void setStateReasonData(String stateReasonData) { this.stateReasonData = stateReasonData; }
-
-    public long getStateUpdatedTimestamp() { return stateUpdatedTimestamp; }
-    public void setStateUpdatedTimestamp(long stateUpdatedTimestamp) { this.stateUpdatedTimestamp = stateUpdatedTimestamp; }

    public String getMetricName() { return metricName; }
    public void setMetricName(String metricName) { this.metricName = metricName; }
@@ -100,8 +46,13 @@ public class MetricAlarm {
    public List<Dimension> getDimensions() { return dimensions; }
    public void setDimensions(List<Dimension> dimensions) { this.dimensions = dimensions; }

-    public int getPeriod() { return period; }
-    public void setPeriod(int period) { this.period = period; }
+    public Integer getPeriod() { return period; }
+    public void setPeriod(Integer period) { this.period = period; }
+
+    public List<AlarmMetricDataQuery> getMetrics() { return metrics; }
+    public void setMetrics(List<AlarmMetricDataQuery> metrics) {
+        this.metrics = metrics == null ? new ArrayList<>() : new ArrayList<>(metrics);
+    }

    public String getUnit() { return unit; }
    public void setUnit(String unit) { this.unit = unit; }
@@ -124,11 +75,4 @@ public class MetricAlarm {
    public String getEvaluateLowSampleCountPercentile() { return evaluateLowSampleCountPercentile; }
    public void setEvaluateLowSampleCountPercentile(String percentile) { this.evaluateLowSampleCountPercentile = percentile; }

-    public Map<String, String> getTags() { return tags; }
-    public void setTags(Map<String, String> tags) { this.tags = tags; }
-
-    /** Not part of the AWS shape; set by {@code putMetricAlarm} so a background evaluator
-     * that only holds the alarm object still knows which region's metric data to query. */
-    public String getRegion() { return region; }
-    public void setRegion(String region) { this.region = region; }
 }
@@ -196,21 +196,30 @@ public class CloudWatchMetricStreamsService {
    }

    public Map<String, String> listTagsForResource(String resourceArn, String region) {
-        return findByArn(resourceArn, region).map(MetricStream::getTags).orElse(Map.of());
+        return requireStream(resourceArn, region).getTags();
    }

    public void tagResource(String resourceArn, Map<String, String> tags, String region) {
-        findByArn(resourceArn, region).ifPresent(stream -> {
-            stream.getTags().putAll(tags);
-            streamStore.put(key(region, stream.getName()), stream);
-        });
+        MetricStream stream = requireStream(resourceArn, region);
+        stream.getTags().putAll(tags);
+        streamStore.put(key(region, stream.getName()), stream);
    }

    public void untagResource(String resourceArn, List<String> tagKeys, String region) {
-        findByArn(resourceArn, region).ifPresent(stream -> {
-            tagKeys.forEach(stream.getTags()::remove);
-            streamStore.put(key(region, stream.getName()), stream);
-        });
+        MetricStream stream = requireStream(resourceArn, region);
+        tagKeys.forEach(stream.getTags()::remove);
+        streamStore.put(key(region, stream.getName()), stream);
+    }
+
+    /**
+     * Resolves the stream an ARN names, or reports that nothing does. The tag operations declare
+     * {@code ResourceNotFoundException}, the same code {@code GetMetricStream} already answers
+     * with, so an unknown ARN here reads the same way an unknown name does.
+     */
+    private MetricStream requireStream(String resourceArn, String region) {
+        return findByArn(resourceArn, region).orElseThrow(() ->
+                new AwsException("ResourceNotFoundException",
+                        "Metric stream " + resourceArn + " does not exist.", 404));
    }

    private Optional<MetricStream> findByArn(String resourceArn, String region) {
@@ -291,7 +291,10 @@ final class CognitoAuthFlowHandler {
            if (!"UserNotFoundException".equals(ae.getErrorCode())) throw ae;
            user = tryUserMigration(pool, client, username, password, null, clientMetadata,
                    "UserMigration_Authentication");
-            if (user == null) throw ae;
+            if (user == null) {
+                if (!CognitoService.hidesUserExistence(client)) throw ae;
+                throw new AwsException("NotAuthorizedException", "Incorrect username or password", 400);
+            }
        }

        firePreAuthentication(pool, client, user, null, clientMetadata, false);
@@ -2592,7 +2592,8 @@ public class CognitoService implements ResourceProvider {
            String confirmationCode) {
        UserPool pool = poolStore.get(userPoolId)
                .orElseThrow(() -> userPoolNotFound(userPoolId));
-        CognitoUser user = adminGetUser(client.getUserPoolId(), username);
+        CognitoUser user = userForClientOrNull(client, username);
+        if (user == null) throw codeMismatch();
        if (verificationCodeService != null && isSignUpConfirmationEnabled(pool)) {
            try {
                verificationCodeService.consume(client.getUserPoolId(), user.getUsername(),
@@ -2636,7 +2637,8 @@ public class CognitoService implements ResourceProvider {
                .orElseThrow(() -> new AwsException("ResourceNotFoundException", "Client not found",
                        400));
        UserPool pool = describeUserPool(client.getUserPoolId());
-        CognitoUser user = adminGetUser(client.getUserPoolId(), username);
+        CognitoUser user = userForClientOrNull(client, username);
+        if (user == null) return simulatedCodeDelivery(username);
        if (!"UNCONFIRMED".equals(user.getUserStatus())) {
            throw new AwsException("NotAuthorizedException",
                    "User cannot be confirmed. Current status is " + user.getUserStatus(), 400);
@@ -2774,7 +2776,8 @@ public class CognitoService implements ResourceProvider {
    public Map<String, Object> forgotPassword(String clientId, String username) {
        UserPoolClient client = clientStore.get(clientId)
                .orElseThrow(() -> new AwsException("ResourceNotFoundException", "Client not found", 400));
-        CognitoUser user = adminGetUser(client.getUserPoolId(), username);
+        CognitoUser user = userForClientOrNull(client, username);
+        if (user == null) return new LinkedHashMap<>(simulatedCodeDelivery(username));
        UserPool pool = describeUserPool(client.getUserPoolId());
        ensureVerificationWiring();
        DeliveryTarget deliveryTarget = resolveForgotPasswordDeliveryTarget(pool, user);
@@ -2800,7 +2803,8 @@ public class CognitoService implements ResourceProvider {
    public void confirmForgotPassword(String clientId, String username, String confirmationCode, String newPassword) {
        UserPoolClient client = clientStore.get(clientId)
                .orElseThrow(() -> new AwsException("ResourceNotFoundException", "Client not found", 400));
-        CognitoUser user = adminGetUser(client.getUserPoolId(), username);
+        CognitoUser user = userForClientOrNull(client, username);
+        if (user == null) throw codeMismatch();
        ensureVerificationWiring();
        try {
            verificationCodeService.consume(client.getUserPoolId(), user.getUsername(),
@@ -3075,6 +3079,18 @@ public class CognitoService implements ResourceProvider {
        return overrideId;
    }

+    /**
+     * The signing keys, by kid, of this emulator's own pool that {@code issuer} names exactly, so a
+     * JWT authorizer can verify the pool's tokens in-process; empty for every other issuer.
+     */
+    public Optional<Map<String, RSAPublicKey>> localIssuerKeys(String issuer) {
+        if (issuer == null) return Optional.empty();
+        String trimmed = issuer.replaceAll("/+$", "");
+        String poolId = trimmed.substring(trimmed.lastIndexOf('/') + 1);
+        if (poolId.isEmpty() || !getIssuer(poolId).equals(trimmed)) return Optional.empty();
+        return poolStore.get(poolId).map(pool -> Map.of(getSigningKeyId(pool), getSigningPublicKey(pool)));
+    }
+
    public String getJwksUri(String poolId) {
        return getIssuer(poolId) + "/.well-known/jwks.json";
    }
@@ -4446,10 +4462,38 @@ public class CognitoService implements ResourceProvider {
        }
    }

+    /**
+     * Whether the app client hides which usernames exist (PreventUserExistenceErrors=ENABLED). Real Cognito then
+     * answers for an unknown user exactly as for a real one: a failed sign-in is "Incorrect username or password",
+     * a code request reports a simulated delivery and a code check reports a wrong code. Unset means LEGACY.
+     */
+    static boolean hidesUserExistence(UserPoolClient client) {
+        return "ENABLED".equals(client.getPreventUserExistenceErrors());
+    }
+
+    /** The user, or null when it does not exist and the client hides that; otherwise UserNotFoundException. */
+    private CognitoUser userForClientOrNull(UserPoolClient client, String username) {
+        try {
+            return adminGetUser(client.getUserPoolId(), username);
+        } catch (AwsException e) {
+            if ("UserNotFoundException".equals(e.getErrorCode()) && hidesUserExistence(client)) return null;
+            throw e;
+        }
+    }
+
+    private Map<String, String> simulatedCodeDelivery(String username) {
+        return username != null && username.contains("@")
+                ? Map.of("AttributeName", "email", "DeliveryMedium", "EMAIL", "Destination", maskEmail(username))
+                : Map.of("AttributeName", "phone_number", "DeliveryMedium", "SMS", "Destination", "+*******0000");
+    }
+
+    private static AwsException codeMismatch() {
+        return new AwsException("CodeMismatchException", "Invalid verification code provided, please try again.", 400);
+    }
+
    private AwsException mapVerificationCodeException(VerificationCodeException e) {
        return switch (e.getKind()) {
-            case MISMATCH, NOT_FOUND -> new AwsException("CodeMismatchException",
-                    "Invalid verification code provided, please try again.", 400);
+            case MISMATCH, NOT_FOUND -> codeMismatch();
            case EXPIRED -> new AwsException("ExpiredCodeException",
                    "Invalid code provided, please request a code again.", 400);
            case RATE_LIMIT -> new AwsException("LimitExceededException",
@@ -57,6 +57,8 @@ public class SmtpRelay {

    private static final Logger LOG = Logger.getLogger(SmtpRelay.class);
    private static final long RELAY_TIMEOUT_SECONDS = 30;
+    /** Every SASL method the mail client supports except XOAUTH2, which expects a token. */
+    static final String PASSWORD_AUTH_METHODS = "CRAM-SHA256 CRAM-SHA1 CRAM-MD5 DIGEST-MD5 LOGIN PLAIN";

    /** SES control header naming the configuration set to apply to a raw send. */
    public static final String HEADER_CONFIGURATION_SET = "X-SES-CONFIGURATION-SET";
@@ -118,6 +120,9 @@ public class SmtpRelay {
                .filter(u -> !u.isBlank())
                .ifPresent(u -> {
                    mailConfig.setUsername(u);
+                    // smtp-pass is a password, never an OAuth token: without this the client prefers
+                    // XOAUTH2 whenever the server offers it (Gmail does) and the login is refused.
+                    mailConfig.setAuthMethods(PASSWORD_AUTH_METHODS);
                    config.services().ses().smtpPass()
                            .filter(p -> !p.isBlank())
                            .ifPresent(mailConfig::setPassword);
@@ -6,11 +6,13 @@ import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.fasterxml.jackson.dataformat.cbor.CBORFactory;
 import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.response.Response;
 import org.junit.jupiter.api.Test;

 import java.time.Instant;

 import static io.restassured.RestAssured.given;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;

@@ -82,6 +84,29 @@ class AwsJsonCborCloudWatchTimestampIntegrationTest {
                        + driftSeconds + "s): " + datapoint);
    }

+    // CloudWatch is awsQueryCompatible: the header keeps the Query code while the body names
+    // the model shape, which is what the AWS SDK v2 uses to pick the typed exception.
+    @Test
+    void putMetricDataWithoutMetricNameReturnsTheModelledExceptionShape() throws Exception {
+        ObjectNode putRequest = JSON.createObjectNode();
+        putRequest.put("Namespace", "CborRpcV2MissingName-" + System.nanoTime());
+        putRequest.putArray("MetricData").addObject().put("Value", 1.0);
+
+        Response response = given()
+                .contentType("application/cbor")
+                .accept("application/cbor")
+                .header("smithy-protocol", "rpc-v2-cbor")
+                .body(AwsJsonCborController.nodeToSmithyCbor(putRequest))
+                .when().post("/service/GraniteServiceVersion20100801/operation/PutMetricData");
+
+        assertEquals(400, response.statusCode());
+        assertEquals("MissingParameter;Sender", response.header("x-amzn-query-error"));
+        JsonNode body = CBOR.readTree(response.asByteArray());
+        assertEquals("MissingRequiredParameterException", body.path("__type").asText(), body.toString());
+        assertEquals("The parameter MetricData.member.1.MetricName is required.",
+                body.path("message").asText(), body.toString());
+    }
+
    private static JsonNode rpcV2Call(String action, ObjectNode body) throws Exception {
        byte[] responseCbor = given()
                .contentType("application/cbor")
@@ -98,6 +98,26 @@ class JwtSignatureVerifierTest {
        verifier.verify(token, issuer); // does not throw
    }

+    @Test
+    void verifiesAnInProcessIssuerWithoutFetchingIt() throws Exception {
+        // Floci's own Cognito issuer: plain HTTP on a hostname, which the strict fetch rules refuse.
+        String localIssuer = "http://floci:4566/us-east-1_local";
+        strictVerifier.withLocalIssuerKeys(candidate -> candidate.equals(localIssuer)
+                ? java.util.Optional.of(Map.of("test-key-1", publicKey)) : java.util.Optional.empty());
+
+        assertDoesNotThrow(() -> strictVerifier.verify(signToken("test-key-1", privateKey), localIssuer));
+        assertThrows(JwtSignatureVerifier.JwtVerificationException.class,
+                () -> strictVerifier.verify(signToken("other-key", privateKey), localIssuer));
+        KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
+        gen.initialize(2048);
+        String forged = signToken("test-key-1", (RSAPrivateKey) gen.generateKeyPair().getPrivate());
+        assertThrows(JwtSignatureVerifier.JwtVerificationException.class,
+                () -> strictVerifier.verify(forged, localIssuer));
+        // Any other plain-HTTP issuer still goes through the strict fetch, and is refused.
+        assertThrows(JwtSignatureVerifier.JwtVerificationException.class,
+                () -> strictVerifier.verify(signToken("test-key-1", privateKey), "http://floci:4566/us-east-1_other"));
+    }
+
    @Test
    void rejectsATokenSignedWithADifferentKey() throws Exception {
        KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA");
@@ -45,6 +45,7 @@ import io.github.hectorvent.floci.services.cloudformation.provisioners.AppSyncCf
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CdkMetadataCfnProvisioner;
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CloudTrailCfnProvisioner;
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CloudWatchCfnProvisioner;
+import io.github.hectorvent.floci.services.cloudformation.provisioners.CloudWatchCompositeAlarmCfnProvisioner;
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CloudWatchDashboardCfnProvisioner;
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CognitoCfnProvisioner;
 import io.github.hectorvent.floci.services.cloudformation.provisioners.CognitoUserPoolGroupCfnProvisioner;
@@ -300,6 +301,7 @@ final class CfnProvisionerFixture {
            }
            if (cloudWatchMetricsService != null) {
                discovered.add(new CloudWatchCfnProvisioner(cloudWatchMetricsService));
+                discovered.add(new CloudWatchCompositeAlarmCfnProvisioner(cloudWatchMetricsService));
            }
            if (cloudWatchDashboardsService != null) {
                discovered.add(new CloudWatchDashboardCfnProvisioner(cloudWatchDashboardsService));
@@ -0,0 +1,190 @@
+package io.github.hectorvent.floci.services.cloudformation;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.testing.CfnStackWaits;
+import io.github.hectorvent.floci.testing.PartitionCleanup;
+import io.github.hectorvent.floci.testing.RestAssuredJsonUtils;
+import io.quarkus.test.common.http.TestHTTPResource;
+import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.response.Response;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.net.URI;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static io.restassured.RestAssured.given;
+import static org.junit.jupiter.api.Assertions.*;
+
+@QuarkusTest
+class CloudFormationCompositeAlarmIntegrationTest {
+    private static final ObjectMapper MAPPER = new ObjectMapper();
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @RegisterExtension
+    final PartitionCleanup cleanup = new PartitionCleanup();
+
+    @BeforeAll
+    static void configureRestAssured() {
+        RestAssuredJsonUtils.configureAwsContentTypes();
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void failedUpdateRestoresRuleTagsAndIdentity(boolean rename) throws Exception {
+        String stack = unique("composite-rollback");
+        String name = stack + "-alarm";
+        String next = rename ? name + "-new" : name;
+        deploy("CreateStack", stack, template(name, "TRUE", Map.of("team", "old", "drop", "restore"), false, false));
+        assertEquals("CREATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        String arn = alarm(name).get("AlarmArn").toString();
+        Response described = given().contentType("application/x-www-form-urlencoded")
+                .formParam("Action", "DescribeStacks").formParam("StackName", stack).post("/");
+        assertEquals(name, described.xmlPath().getString(
+                "DescribeStacksResponse.DescribeStacksResult.Stacks.member.Outputs.member.find { it.OutputKey == 'Name' }.OutputValue"));
+        assertEquals(arn, described.xmlPath().getString(
+                "DescribeStacksResponse.DescribeStacksResult.Stacks.member.Outputs.member.find { it.OutputKey == 'Arn' }.OutputValue"));
+        cw("TagResource", Map.of("ResourceARN", arn, "Tags", List.of(Map.of("Key", "external", "Value", "keep"))))
+                .then().statusCode(200);
+        deploy("UpdateStack", stack, template(next, "FALSE", Map.of("team", "new", "added", "remove"), true, false));
+        assertEquals("UPDATE_ROLLBACK_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        assertEquals("TRUE", alarm(name).get("AlarmRule"));
+        List<Map<String, String>> tags = cw("ListTagsForResource", Map.of("ResourceARN", arn))
+                .then().statusCode(200).extract().jsonPath().getList("Tags");
+        assertEquals(Map.of("team", "old", "drop", "restore", "external", "keep"),
+                tags.stream().collect(Collectors.toMap(t -> t.get("Key"), t -> t.get("Value"))));
+        if (rename) {
+            assertMissing(next);
+        }
+        deleteStack(stack);
+        assertMissing(name);
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void replacementHonorsRetentionAndDeletesItsCurrentBackingAlarm(boolean retain) throws Exception {
+        String stack = unique("composite-replace");
+        String original = stack + "-old";
+        String next = stack + "-new";
+        deploy("CreateStack", stack, template(original, "TRUE", Map.of(), false, retain));
+        assertEquals("CREATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        deploy("UpdateStack", stack, template(next, "FALSE", Map.of(), false, retain));
+        assertEquals("UPDATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        assertEquals("FALSE", alarm(next).get("AlarmRule"));
+        if (retain) {
+            assertEquals("TRUE", alarm(original).get("AlarmRule"));
+        } else {
+            assertMissing(original);
+        }
+        deleteStack(stack);
+        assertMissing(next);
+        if (retain) {
+            assertEquals("TRUE", alarm(original).get("AlarmRule"));
+            cw("DeleteAlarms", Map.of("AlarmNames", List.of(original))).then().statusCode(200);
+        }
+    }
+
+    @Test
+    void committedInPlaceUpdatesAllowAnotherUpdateAndReplacement() throws Exception {
+        String stack = unique("composite-sequence");
+        String name = stack + "-alarm";
+        String replacement = name + "-new";
+        deploy("CreateStack", stack, template(name, "TRUE", Map.of("team", "initial"), false, false));
+        assertEquals("CREATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        for (String rule : List.of("FALSE", "TRUE")) {
+            deploy("UpdateStack", stack, template(name, rule, Map.of("team", rule), false, false));
+            assertEquals("UPDATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+            assertEquals(rule, alarm(name).get("AlarmRule"));
+        }
+        deploy("UpdateStack", stack, template(replacement, "FALSE", Map.of(), false, false));
+        assertEquals("UPDATE_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        assertMissing(name);
+        assertEquals("FALSE", alarm(replacement).get("AlarmRule"));
+        deleteStack(stack);
+        assertMissing(replacement);
+    }
+
+    @Test
+    void createCollisionCannotOverwriteOrDeleteAnUnmanagedAlarm() throws Exception {
+        String stack = unique("composite-foreign");
+        String name = stack + "-alarm";
+        cw("PutCompositeAlarm", Map.of("AlarmName", name, "AlarmRule", "TRUE")).then().statusCode(200);
+        deploy("CreateStack", stack, template(name, "FALSE", Map.of(), false, false));
+        assertEquals("ROLLBACK_COMPLETE", CfnStackWaits.awaitTerminal(stack).status());
+        assertEquals("TRUE", alarm(name).get("AlarmRule"));
+        deleteStack(stack);
+        assertEquals("TRUE", alarm(name).get("AlarmRule"));
+        cw("DeleteAlarms", Map.of("AlarmNames", List.of(name))).then().statusCode(200);
+    }
+
+    private String template(String name, String rule, Map<String, String> tags, boolean fail, boolean retain)
+            throws JsonProcessingException {
+        cleanup.register(() -> cw("DeleteAlarms", Map.of("AlarmNames", List.of(name))).then().statusCode(200));
+        Map<String, Object> resources = new LinkedHashMap<>();
+        resources.put("Alarm", Map.of("Type", "AWS::CloudWatch::CompositeAlarm",
+                "UpdateReplacePolicy", retain ? "Retain" : "Delete",
+                "Properties", Map.of("AlarmName", name, "AlarmRule", rule,
+                        "Tags", tags.entrySet().stream().map(e -> Map.of("Key", e.getKey(), "Value", e.getValue())).toList())));
+        if (fail) {
+            resources.put("Failure", Map.of("Type", "AWS::SecretsManager::Secret", "DependsOn", "Alarm",
+                    "Properties", Map.of("SecretString", "explicit", "GenerateSecretString", Map.of("PasswordLength", 32))));
+        }
+        return MAPPER.writeValueAsString(Map.of("Resources", resources, "Outputs", Map.of(
+                "Name", Map.of("Value", Map.of("Ref", "Alarm")),
+                "Arn", Map.of("Value", Map.of("Fn::GetAtt", List.of("Alarm", "Arn"))))));
+    }
+
+    private void deploy(String action, String stack, String template) {
+        if ("CreateStack".equals(action)) {
+            cleanup.register(() -> given().port(baseUri.getPort())
+                    .contentType("application/x-www-form-urlencoded")
+                    .formParam("Action", "DeleteStack").formParam("StackName", stack)
+                    .post("/").then().statusCode(200));
+        }
+        given().contentType("application/x-www-form-urlencoded").formParam("Action", action)
+                .formParam("StackName", stack).formParam("TemplateBody", template).post("/").then().statusCode(200);
+    }
+
+    private Response cw(String operation, Map<String, ?> body) {
+        if ("PutCompositeAlarm".equals(operation)) {
+            String name = body.get("AlarmName").toString();
+            cleanup.register(() -> cw("DeleteAlarms", Map.of("AlarmNames", List.of(name))).then().statusCode(200));
+        }
+        return given().port(baseUri.getPort()).contentType("application/x-amz-json-1.0")
+                .header("X-Amz-Target", "GraniteServiceVersion20100801." + operation)
+                .body(MAPPER.valueToTree(body).toString()).post("/");
+    }
+
+    private Map<String, Object> alarm(String name) throws JsonProcessingException {
+        List<Map<String, Object>> alarms = cw("DescribeAlarms", Map.of("AlarmNames", List.of(name),
+                "AlarmTypes", List.of("CompositeAlarm"))).then().statusCode(200)
+                .extract().jsonPath().getList("CompositeAlarms");
+        assertEquals(1, alarms.size(), name);
+        return alarms.getFirst();
+    }
+
+    private void assertMissing(String name) throws JsonProcessingException {
+        assertEquals(List.of(), cw("DescribeAlarms", Map.of("AlarmNames", List.of(name),
+                "AlarmTypes", List.of("CompositeAlarm"))).then().statusCode(200)
+                .extract().jsonPath().getList("CompositeAlarms"));
+    }
+
+    private void deleteStack(String stack) {
+        given().contentType("application/x-www-form-urlencoded").formParam("Action", "DeleteStack")
+                .formParam("StackName", stack).post("/").then().statusCode(200);
+        CfnStackWaits.awaitStackDeleted(stack);
+    }
+
+    private static String unique(String prefix) {
+        return prefix + "-" + Long.toString(System.nanoTime(), 36);
+    }
+}
@@ -0,0 +1,89 @@
+package io.github.hectorvent.floci.services.cloudformation.provisioners;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.core.common.AwsException;
+import io.github.hectorvent.floci.services.cloudformation.CloudFormationTemplateEngine;
+import io.github.hectorvent.floci.services.cloudformation.model.StackResource;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.CloudWatchMetricsService;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.*;
+import static org.mockito.Mockito.*;
+
+class CloudWatchCompositeAlarmCfnProvisionerTest {
+    @Test
+    void rejectedBackingUpdateDoesNotArmRollbackToDeleteAnUnmanagedReplacement() throws Exception {
+        CloudWatchMetricsService service = mock(CloudWatchMetricsService.class);
+        CloudWatchCompositeAlarmCfnProvisioner provisioner = new CloudWatchCompositeAlarmCfnProvisioner(service);
+        CloudFormationTemplateEngine engine = mock(CloudFormationTemplateEngine.class);
+        when(engine.resolve(any())).thenAnswer(call -> {
+            JsonNode node = call.getArgument(0);
+            return node == null || node.isMissingNode() ? null : node.asText();
+        });
+        when(engine.resolveNode(any())).thenAnswer(call -> call.getArgument(0));
+        StackResource resource = new StackResource();
+        resource.setLogicalId("Alarm");
+        resource.setResourceType("AWS::CloudWatch::CompositeAlarm");
+        resource.setPhysicalId("kept");
+        resource.getAttributes().put("Arn", "prior-arn");
+        AwsException collision = new AwsException("ValidationError", "A metric alarm now has this name", 400);
+        doThrow(collision).when(service).putCompositeAlarm(any(), eq("us-east-1"), eq(true));
+        ProvisionContext context = new ProvisionContext(engine, "us-east-1", "000000000000", "stack", "kept");
+        JsonNode props = new ObjectMapper().readTree("{\"AlarmName\":\"kept\",\"AlarmRule\":\"TRUE\"}");
+        assertSame(collision, assertThrows(AwsException.class, () -> provisioner.provision(resource, props, context)));
+        assertFalse(provisioner.retainsFailedUpdateState(resource));
+        assertFalse(provisioner.rollbackUpdate(resource));
+        assertEquals("kept", resource.getPhysicalId());
+        assertEquals(Map.of("Arn", "prior-arn"), resource.getAttributes());
+        verify(service, never()).deleteAlarms(any(), anyString());
+    }
+
+    @Test
+    void inPlaceUpdateRetriesPreviouslyDisplacedAlarmCleanup() throws Exception {
+        CloudWatchMetricsService service = mock(CloudWatchMetricsService.class);
+        CloudWatchCompositeAlarmCfnProvisioner provisioner = new CloudWatchCompositeAlarmCfnProvisioner(service);
+        CloudFormationTemplateEngine engine = mock(CloudFormationTemplateEngine.class);
+        when(engine.resolve(any())).thenAnswer(call -> {
+            JsonNode node = call.getArgument(0);
+            return node == null || node.isMissingNode() ? null : node.asText();
+        });
+        when(engine.resolveNode(any())).thenAnswer(call -> call.getArgument(0));
+        StackResource resource = new StackResource();
+        resource.setLogicalId("Alarm");
+        resource.setResourceType("AWS::CloudWatch::CompositeAlarm");
+        resource.setPhysicalId("current");
+        ReplacementCleanup.record(resource,
+                new ProvisionContext(engine, "us-east-1", "000000000000", "stack", "displaced"), Map.of());
+        doThrow(new IllegalStateException("delete unavailable"))
+                .doThrow(new IllegalStateException("delete still unavailable")).doNothing()
+                .when(service).deleteAlarms(List.of("displaced"), "us-east-1");
+        assertFalse(provisioner.completeUpdate(resource).complete());
+        provisioner.clearUpdate(resource);
+        assertEquals(Set.of("displaced"), ReplacementCleanup.owedPhysicalIds(resource));
+
+        ProvisionContext context = new ProvisionContext(engine, "us-east-1", "000000000000", "stack", "current");
+        JsonNode props = new ObjectMapper().readTree("{\"AlarmName\":\"current\",\"AlarmRule\":\"TRUE\"}");
+        provisioner.provision(resource, props, context);
+        assertTrue(provisioner.retainsFailedUpdateState(resource));
+        UpdateCleanupResult retry = provisioner.completeUpdate(resource);
+        assertFalse(retry.complete());
+        assertEquals(2, retry.attempts());
+        assertEquals("displaced", retry.previousPhysicalId());
+        assertEquals("delete still unavailable", retry.failureReason());
+        assertEquals(Set.of("displaced"), ReplacementCleanup.owedPhysicalIds(resource));
+        assertTrue(provisioner.completeUpdate(resource).complete());
+        provisioner.clearUpdate(resource);
+        assertFalse(provisioner.retainsFailedUpdateState(resource));
+        assertTrue(ReplacementCleanup.owedPhysicalIds(resource).isEmpty());
+        assertEquals("current", resource.getPhysicalId());
+        verify(service, times(3)).deleteAlarms(List.of("displaced"), "us-east-1");
+        verify(service, never()).deleteAlarms(List.of("current"), "us-east-1");
+    }
+
+}
@@ -0,0 +1,349 @@
+package io.github.hectorvent.floci.services.cloudwatch;
+
+import io.github.hectorvent.floci.testing.RestAssuredJsonUtils;
+import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.specification.RequestSpecification;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static io.restassured.RestAssured.given;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
+
+/**
+ * Tagging a CloudWatch resource whose ARN names nothing has to fail, on every one of the three
+ * tag operations and for every taggable kind CloudWatch owns.
+ *
+ * <p>Each kind is checked twice: once on an ARN that resolves, so the operation is known to work
+ * at all, and once on the same ARN with the resource name swapped for one that was never created.
+ * The two ARNs are byte-identical in shape, so "the ARN was malformed" cannot explain the second
+ * answer. Without that pairing a test asserting only the failure would also pass against a build
+ * whose tag operations were broken outright.
+ *
+ * <p>The failure to look for is {@code ResourceNotFoundException}. CloudWatch's model declares
+ * that code, not the shorter {@code ResourceNotFound} that {@code GetDashboard} and
+ * {@code SetAlarmState} answer with, for {@code TagResource}, {@code UntagResource} and
+ * {@code ListTagsForResource}; the SDK maps the two to different exception classes, so a caller
+ * catching the documented one would not see the other.
+ */
+@QuarkusTest
+class CloudWatchTagUnknownResourceIntegrationTest {
+
+    private static final String CW_SCOPE =
+            "AWS4-HMAC-SHA256 Credential=test/20260205/us-east-1/monitoring/aws4_request";
+    private static final String LOGS_SCOPE =
+            "AWS4-HMAC-SHA256 Credential=test/20260205/us-east-1/logs/aws4_request";
+
+    private static final String JSON_1_0 = "application/x-amz-json-1.0";
+    private static final String JSON_1_1 = "application/x-amz-json-1.1";
+
+    private static final String PREFIX = "arn:aws:cloudwatch:us-east-1:000000000000:";
+    private static final String FIREHOSE_ARN =
+            "arn:aws:firehose:us-east-1:000000000000:deliverystream/metrics";
+    private static final String ROLE_ARN = "arn:aws:iam::000000000000:role/metric-stream-role";
+
+    @BeforeAll
+    static void configureRestAssured() {
+        RestAssuredJsonUtils.configureAwsContentTypes();
+    }
+
+    private static RequestSpecification query(String action) {
+        return given()
+                .contentType("application/x-www-form-urlencoded")
+                .header("Authorization", CW_SCOPE)
+                .formParam("Action", action);
+    }
+
+    private static RequestSpecification json(String contentType, String scope, String target, String body) {
+        return given()
+                .contentType(contentType)
+                .header("Authorization", scope)
+                .header("X-Amz-Target", target)
+                .body(body);
+    }
+
+    private static RequestSpecification metricsJson(String target, String body) {
+        return json(JSON_1_0, CW_SCOPE, "GraniteServiceVersion20100801." + target, body);
+    }
+
+    private static RequestSpecification logsJson(String target, String body) {
+        return json(JSON_1_1, LOGS_SCOPE, "Logs_20140328." + target, body);
+    }
+
+    /** The three Query tag operations against one ARN, asserting the same outcome for each. */
+    private static void assertQueryTagOpsNotFound(String arn) {
+        query("TagResource")
+                .formParam("ResourceARN", arn)
+                .formParam("Tags.member.1.Key", "env")
+                .formParam("Tags.member.1.Value", "prod")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("ErrorResponse.Error.Code", equalTo("ResourceNotFoundException"));
+
+        query("UntagResource")
+                .formParam("ResourceARN", arn)
+                .formParam("TagKeys.member.1", "env")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("ErrorResponse.Error.Code", equalTo("ResourceNotFoundException"));
+
+        query("ListTagsForResource")
+                .formParam("ResourceARN", arn)
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("ErrorResponse.Error.Code", equalTo("ResourceNotFoundException"));
+    }
+
+    /** The same three operations against an ARN that does resolve, read back through a list. */
+    private static void assertQueryTagOpsSucceed(String arn) {
+        query("TagResource")
+                .formParam("ResourceARN", arn)
+                .formParam("Tags.member.1.Key", "env")
+                .formParam("Tags.member.1.Value", "prod")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        query("ListTagsForResource")
+                .formParam("ResourceARN", arn)
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200)
+                .body("ListTagsForResourceResponse.ListTagsForResourceResult.Tags.member.Key",
+                        equalTo("env"))
+                .body("ListTagsForResourceResponse.ListTagsForResourceResult.Tags.member.Value",
+                        equalTo("prod"));
+
+        query("UntagResource")
+                .formParam("ResourceARN", arn)
+                .formParam("TagKeys.member.1", "env")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        query("ListTagsForResource")
+                .formParam("ResourceARN", arn)
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200)
+                .body(not(containsString("<Key>env</Key>")));
+    }
+
+    @Test
+    void alarmTagOperationsRejectAnArnThatNamesNoAlarm() {
+        query("PutMetricAlarm")
+                .formParam("AlarmName", "tag-unknown-alarm")
+                .formParam("MetricName", "CPUUtilization")
+                .formParam("Namespace", "AWS/EC2")
+                .formParam("ComparisonOperator", "GreaterThanThreshold")
+                .formParam("EvaluationPeriods", "1")
+                .formParam("Period", "60")
+                .formParam("Statistic", "Average")
+                .formParam("Threshold", "80")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        assertQueryTagOpsSucceed(PREFIX + "alarm:tag-unknown-alarm");
+        assertQueryTagOpsNotFound(PREFIX + "alarm:tag-unknown-alarm-nosuch");
+    }
+
+    @Test
+    void dashboardTagOperationsRejectAnArnThatNamesNoDashboard() {
+        query("PutDashboard")
+                .formParam("DashboardName", "tag-unknown-dashboard")
+                .formParam("DashboardBody", "{\"widgets\":[]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        assertQueryTagOpsSucceed(PREFIX + "dashboard/tag-unknown-dashboard");
+        assertQueryTagOpsNotFound(PREFIX + "dashboard/tag-unknown-dashboard-nosuch");
+    }
+
+    @Test
+    void metricStreamTagOperationsRejectAnArnThatNamesNoStream() {
+        query("PutMetricStream")
+                .formParam("Name", "tag-unknown-stream")
+                .formParam("FirehoseArn", FIREHOSE_ARN)
+                .formParam("RoleArn", ROLE_ARN)
+                .formParam("OutputFormat", "json")
+                .formParam("IncludeFilters.member.1.Namespace", "AWS/EC2")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        assertQueryTagOpsSucceed(PREFIX + "metric-stream/tag-unknown-stream");
+        assertQueryTagOpsNotFound(PREFIX + "metric-stream/tag-unknown-stream-nosuch");
+    }
+
+    /**
+     * The dashboard ARN AWS documents carries no region, and the one Floci mints does. A
+     * caller sending the documented form for a dashboard that exists must not be told the
+     * dashboard does not exist, which is what raising on a miss would otherwise have made of
+     * a shape that used to fall through to an empty tag map.
+     */
+    @Test
+    void theRegionlessDashboardArnAwsDocumentsAlsoResolves() {
+        query("PutDashboard")
+                .formParam("DashboardName", "tag-regionless-dashboard")
+                .formParam("DashboardBody", "{\"widgets\":[]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        assertQueryTagOpsSucceed("arn:aws:cloudwatch::000000000000:dashboard/tag-regionless-dashboard");
+
+        // Still only an absent region: another region's ARN remains a miss.
+        assertQueryTagOpsNotFound(
+                "arn:aws:cloudwatch:eu-west-1:000000000000:dashboard/tag-regionless-dashboard");
+    }
+
+    /**
+     * Both handlers route every ARN that is not a dashboard and not a metric stream to the
+     * alarm path, so a Contributor Insights ARN, which AWS documents as taggable and Floci
+     * does not serve, lands there. Reporting it as not found is right; calling it an alarm
+     * that was not found is not, so the message names the ARN instead.
+     */
+    @Test
+    void anArnOfAKindFlociDoesNotServeIsReportedAgainstTheArn() {
+        query("TagResource")
+                .formParam("ResourceARN", PREFIX + "insight-rule/no-such-rule")
+                .formParam("Tags.member.1.Key", "env")
+                .formParam("Tags.member.1.Value", "prod")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("ErrorResponse.Error.Code", equalTo("ResourceNotFoundException"))
+                .body("ErrorResponse.Error.Message",
+                        containsString("insight-rule/no-such-rule"))
+                .body("ErrorResponse.Error.Message",
+                        not(containsString("Alarm")));
+    }
+
+    /**
+     * CloudWatch Metrics serves the same three operations over JSON as well as Query, and
+     * AGENTS.md requires the two handlers not to drift. A fix applied to only one of them
+     * would leave the CLI and SDK v3 route still answering 200.
+     */
+    @Test
+    void theJsonProtocolRejectsTheSameArns() {
+        metricsJson("PutMetricAlarm", """
+                {"AlarmName": "tag-unknown-json-alarm", "MetricName": "CPUUtilization",
+                 "Namespace": "AWS/EC2", "ComparisonOperator": "GreaterThanThreshold",
+                 "EvaluationPeriods": 1, "Period": 60, "Statistic": "Average", "Threshold": 80}""")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        String real = PREFIX + "alarm:tag-unknown-json-alarm";
+        String ghost = PREFIX + "alarm:tag-unknown-json-alarm-nosuch";
+
+        metricsJson("TagResource",
+                "{\"ResourceARN\": \"" + real + "\", \"Tags\": [{\"Key\": \"env\", \"Value\": \"prod\"}]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        metricsJson("ListTagsForResource", "{\"ResourceARN\": \"" + real + "\"}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200)
+                .body("Tags[0].Key", equalTo("env"))
+                .body("Tags[0].Value", equalTo("prod"));
+
+        metricsJson("TagResource",
+                "{\"ResourceARN\": \"" + ghost + "\", \"Tags\": [{\"Key\": \"env\", \"Value\": \"prod\"}]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("__type", containsString("ResourceNotFoundException"));
+
+        metricsJson("UntagResource", "{\"ResourceARN\": \"" + ghost + "\", \"TagKeys\": [\"env\"]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("__type", containsString("ResourceNotFoundException"));
+
+        metricsJson("ListTagsForResource", "{\"ResourceARN\": \"" + ghost + "\"}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(404)
+                .body("__type", containsString("ResourceNotFoundException"));
+    }
+
+    /**
+     * CloudWatch Logs serves its own TagResource, UntagResource and ListTagsForResource over
+     * a separate handler, and already rejects an ARN that names no log group. Pinning it keeps
+     * the two halves of CloudWatch's tagging from diverging again in the other direction.
+     */
+    @Test
+    void logGroupTagOperationsRejectAnArnThatNamesNoGroup() {
+        String real = "arn:aws:logs:us-east-1:000000000000:log-group:tag-unknown-group:*";
+        String ghost = "arn:aws:logs:us-east-1:000000000000:log-group:tag-unknown-group-nosuch:*";
+
+        logsJson("CreateLogGroup", "{\"logGroupName\": \"tag-unknown-group\"}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        logsJson("TagResource",
+                "{\"resourceArn\": \"" + real + "\", \"tags\": {\"env\": \"prod\"}}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200);
+
+        logsJson("ListTagsForResource", "{\"resourceArn\": \"" + real + "\"}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(200)
+                .body("tags.env", equalTo("prod"));
+
+        logsJson("TagResource",
+                "{\"resourceArn\": \"" + ghost + "\", \"tags\": {\"env\": \"prod\"}}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(400)
+                .body("__type", containsString("ResourceNotFoundException"));
+
+        logsJson("UntagResource", "{\"resourceArn\": \"" + ghost + "\", \"tagKeys\": [\"env\"]}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(400)
+                .body("__type", containsString("ResourceNotFoundException"));
+
+        logsJson("ListTagsForResource", "{\"resourceArn\": \"" + ghost + "\"}")
+            .when()
+                .post("/")
+            .then()
+                .statusCode(400)
+                .body("__type", containsString("ResourceNotFoundException"));
+    }
+}
@@ -8,6 +8,7 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;

 import java.util.List;
+import java.util.Map;

 import static org.junit.jupiter.api.Assertions.*;

@@ -116,10 +117,10 @@ class CloudWatchDashboardsServiceTest {

    @Test
    void tagsGivenOnCreateAreReadableByArn() {
-        service.putDashboard("ops", BODY, java.util.Map.of("team", "platform"), REGION);
+        service.putDashboard("ops", BODY, Map.of("team", "platform"), REGION);
        String arn = service.getDashboard("ops", REGION).getDashboardArn();

-        assertEquals(java.util.Map.of("team", "platform"), service.listTagsForResource(arn, REGION));
+        assertEquals(Map.of("team", "platform"), service.listTagsForResource(arn, REGION));
        assertTrue(CloudWatchDashboardsService.isDashboardArn(arn));
    }

@@ -129,12 +130,12 @@ class CloudWatchDashboardsServiceTest {
     */
    @Test
    void tagsOnAReplacingPutDoNotOverwriteTheExistingOnes() {
-        service.putDashboard("ops", BODY, java.util.Map.of("team", "platform"), REGION);
+        service.putDashboard("ops", BODY, Map.of("team", "platform"), REGION);
        String arn = service.getDashboard("ops", REGION).getDashboardArn();

-        service.putDashboard("ops", BODY, java.util.Map.of("team", "someone-else"), REGION);
+        service.putDashboard("ops", BODY, Map.of("team", "someone-else"), REGION);

-        assertEquals(java.util.Map.of("team", "platform"), service.listTagsForResource(arn, REGION));
+        assertEquals(Map.of("team", "platform"), service.listTagsForResource(arn, REGION));
    }

    @Test
@@ -142,11 +143,75 @@ class CloudWatchDashboardsServiceTest {
        service.putDashboard("ops", BODY, REGION);
        String arn = service.getDashboard("ops", REGION).getDashboardArn();

-        service.tagResource(arn, java.util.Map.of("env", "dev"), REGION);
-        assertEquals(java.util.Map.of("env", "dev"), service.listTagsForResource(arn, REGION));
+        service.tagResource(arn, Map.of("env", "dev"), REGION);
+        assertEquals(Map.of("env", "dev"), service.listTagsForResource(arn, REGION));

        service.untagResource(arn, List.of("env"), REGION);
-        assertEquals(java.util.Map.of(), service.listTagsForResource(arn, REGION));
+        assertEquals(Map.of(), service.listTagsForResource(arn, REGION));
+    }
+
+    /**
+     * AWS documents the dashboard ARN without a region and Floci mints one with a region, so
+     * both forms have to resolve. Before the tag operations raised on a miss this divergence
+     * was invisible here: the documented ARN matched nothing and got an empty tag map back.
+     */
+    @Test
+    void bothTheRegionlessAndTheRegionfulDashboardArnResolve() {
+        service.putDashboard("ops", BODY, REGION);
+        String regionful = service.getDashboard("ops", REGION).getDashboardArn();
+        String regionless = "arn:aws:cloudwatch::000000000000:dashboard/ops";
+
+        assertEquals("arn:aws:cloudwatch:us-east-1:000000000000:dashboard/ops", regionful);
+        assertTrue(CloudWatchDashboardsService.isDashboardArn(regionless));
+
+        service.tagResource(regionless, Map.of("env", "dev"), REGION);
+        // Read back through the other form: one dashboard, reachable either way.
+        assertEquals(Map.of("env", "dev"), service.listTagsForResource(regionful, REGION));
+        assertEquals(Map.of("env", "dev"), service.listTagsForResource(regionless, REGION));
+
+        service.untagResource(regionless, List.of("env"), REGION);
+        assertEquals(Map.of(), service.listTagsForResource(regionful, REGION));
+    }
+
+    /**
+     * Only an absent region stands in for the dashboard's own. An ARN naming a different
+     * region must not resolve to the same-named dashboard in this one.
+     */
+    @Test
+    void anArnNamingAnotherRegionDoesNotResolve() {
+        service.putDashboard("ops", BODY, REGION);
+        String elsewhere = "arn:aws:cloudwatch:eu-west-1:000000000000:dashboard/ops";
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> service.listTagsForResource(elsewhere, REGION));
+        assertEquals("ResourceNotFoundException", e.getErrorCode());
+    }
+
+    /**
+     * An ARN naming no dashboard is an error on all three operations, not a silent no-op. The
+     * ARN used here differs from a working one only in the dashboard name, so the outcome
+     * cannot be explained by the ARN failing to parse as a dashboard ARN.
+     */
+    @Test
+    void tagOperationsRejectAnArnThatNamesNoDashboard() {
+        service.putDashboard("ops", BODY, REGION);
+        String arn = service.getDashboard("ops", REGION).getDashboardArn();
+        String ghost = arn.replace("dashboard/ops", "dashboard/nosuch");
+        assertTrue(CloudWatchDashboardsService.isDashboardArn(ghost));
+
+        for (Runnable call : List.<Runnable>of(
+                () -> service.tagResource(ghost, Map.of("env", "prod"), REGION),
+                () -> service.untagResource(ghost, List.of("env"), REGION),
+                () -> service.listTagsForResource(ghost, REGION))) {
+            AwsException e = assertThrows(AwsException.class, call::run);
+            assertEquals("ResourceNotFoundException", e.getErrorCode());
+            assertEquals(404, e.getHttpStatus());
+        }
+
+        // The failures wrote nothing: the real dashboard still carries only what it was given.
+        assertEquals(Map.of(), service.listTagsForResource(arn, REGION));
+        service.tagResource(arn, Map.of("env", "dev"), REGION);
+        assertEquals(Map.of("env", "dev"), service.listTagsForResource(arn, REGION));
    }

    @Test
@@ -0,0 +1,170 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.core.common.RegionResolver;
+import io.github.hectorvent.floci.core.storage.InMemoryStorage;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.services.sns.SnsService;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.*;
+import static org.mockito.Mockito.*;
+
+class AlarmSnsNotifierTest {
+    private static final String REGION = "us-east-1";
+    private static final String TOPIC = "arn:aws:sns:us-east-1:000000000000:alarms";
+    private final ObjectMapper mapper = new ObjectMapper();
+    private SnsService sns;
+    private CloudWatchMetricsService service;
+    private MetricAlarm alarm;
+
+    @BeforeEach
+    void setUp() {
+        sns = mock(SnsService.class);
+        service = new CloudWatchMetricsService(new InMemoryStorage<>(), new InMemoryStorage<>(),
+                new RegionResolver(REGION, "000000000000"), new AlarmSnsNotifier(sns, mapper));
+        alarm = new MetricAlarm();
+        alarm.setAlarmName("test-alarm");
+        alarm.setActionsEnabled(true);
+        alarm.setAlarmActions(List.of(TOPIC));
+        alarm.setOkActions(List.of(TOPIC));
+        alarm.setInsufficientDataActions(List.of(TOPIC));
+        alarm.setEvaluationPeriods(3);
+        alarm.setStatistic("Average");
+        alarm.setMetricName("Errors");
+        alarm.setNamespace("Local/PoC");
+        service.putMetricAlarm(alarm, REGION);
+    }
+
+    @Test
+    void publishesAwsPayloadForEachTransitionButNotRepeatedState() throws Exception {
+        service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION);
+        service.setAlarmState("test-alarm", "ALARM", "still breached", null, REGION);
+        service.setAlarmState("test-alarm", "OK", "recovered", null, REGION);
+        service.setAlarmState("test-alarm", "INSUFFICIENT_DATA", "missing", null, REGION);
+        ArgumentCaptor<String> messages = ArgumentCaptor.forClass(String.class);
+        verify(sns, times(3)).publish(eq(TOPIC), isNull(), messages.capture(), anyString(), eq(REGION));
+        JsonNode first = mapper.readTree(messages.getAllValues().getFirst());
+        assertEquals("test-alarm", first.path("AlarmName").asText());
+        assertEquals("INSUFFICIENT_DATA", first.path("OldStateValue").asText());
+        assertEquals("ALARM", first.path("NewStateValue").asText());
+        assertEquals("000000000000", first.path("AWSAccountId").asText());
+        assertEquals(alarm.getAlarmArn(), first.path("AlarmArn").asText());
+        assertEquals("Errors", first.path("Trigger").path("MetricName").asText());
+        assertFalse(first.path("Trigger").has("DatapointsToAlarm"));
+        assertEquals("AVERAGE", first.path("Trigger").path("Statistic").asText());
+        assertEquals("", first.path("Trigger").path("EvaluateLowSampleCountPercentile").asText());
+        assertTrue(first.path("Trigger").path("EvaluateLowSampleCountPercentile").isTextual());
+        assertNull(alarm.getDatapointsToAlarm());
+        assertEquals("OK", mapper.readTree(messages.getAllValues().get(2)).path("OldStateValue").asText());
+    }
+
+    @Test
+    void formatsBothTimestampsWithMillisAndUtcOffset() throws Exception {
+        alarm.setAlarmConfigurationUpdatedTimestamp(1716280510L);
+        service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION);
+        ArgumentCaptor<String> message = ArgumentCaptor.forClass(String.class);
+        verify(sns).publish(eq(TOPIC), isNull(), message.capture(), anyString(), eq(REGION));
+        JsonNode payload = mapper.readTree(message.getValue());
+        assertEquals("2024-05-21T08:35:10.000+0000",
+                payload.path("AlarmConfigurationUpdatedTimestamp").asText());
+        String stateChangeTime = payload.path("StateChangeTime").asText();
+        assertTrue(stateChangeTime
+                .matches("[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}\\.[0-9]{3}\\+0000"));
+        assertEquals(alarm.getStateUpdatedTimestamp(),
+                Instant.parse(stateChangeTime.replace("+0000", "Z")).getEpochSecond());
+    }
+
+    @Test
+    void preservesExplicitDatapointsToAlarmInPayload() throws Exception {
+        alarm.setDatapointsToAlarm(2);
+        alarm.setStatistic("Maximum");
+        alarm.setEvaluateLowSampleCountPercentile("ignore");
+        service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION);
+        ArgumentCaptor<String> message = ArgumentCaptor.forClass(String.class);
+        verify(sns).publish(eq(TOPIC), isNull(), message.capture(), anyString(), eq(REGION));
+        assertEquals(2, mapper.readTree(message.getValue()).path("Trigger").path("DatapointsToAlarm").intValue());
+        JsonNode trigger = mapper.readTree(message.getValue()).path("Trigger");
+        assertEquals("MAXIMUM", trigger.path("Statistic").asText());
+        assertEquals("ignore", trigger.path("EvaluateLowSampleCountPercentile").asText());
+        assertEquals(2, alarm.getDatapointsToAlarm());
+    }
+
+    @Test
+    void disabledActionsDoNotPublish() {
+        alarm.setActionsEnabled(false);
+        service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION);
+        verifyNoInteractions(sns);
+        assertEquals("ALARM", alarm.getStateValue());
+    }
+
+    @Test
+    void failedTargetDoesNotPreventOtherTargetsOrStateChange() {
+        String missing = "arn:aws:sns:us-east-1:000000000000:missing";
+        alarm.setAlarmActions(List.of(missing, "arn:aws:autoscaling:us-east-1:000000000000:scalingPolicy:x", TOPIC));
+        doThrow(new IllegalStateException("missing topic"))
+                .when(sns).publish(eq(missing), isNull(), anyString(), anyString(), eq(REGION));
+        assertDoesNotThrow(() -> service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION));
+        verify(sns).publish(eq(TOPIC), isNull(), anyString(), anyString(), eq(REGION));
+        assertEquals("ALARM", alarm.getStateValue());
+    }
+
+    @Test
+    void usesTopicRegionAndPreservesChinaPartition() {
+        String topic = "arn:aws-cn:sns:cn-north-1:000000000000:alarms";
+        alarm.setAlarmArn("arn:aws-cn:cloudwatch:cn-north-1:000000000000:alarm:test-alarm");
+        alarm.setAlarmActions(List.of(topic));
+        service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION);
+        verify(sns).publish(eq(topic), isNull(), contains("arn:aws-cn:cloudwatch:"), anyString(), eq("cn-north-1"));
+    }
+
+    @Test
+    void blockedNotificationDoesNotHoldTheAlarmMutationLock() throws Exception {
+        CountDownLatch publishing = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        doAnswer(call -> {
+            if (call.<String>getArgument(3).startsWith("ALARM:")) {
+                publishing.countDown();
+                assertTrue(release.await(5, TimeUnit.SECONDS));
+            }
+            return "message-id";
+        }).when(sns).publish(eq(TOPIC), isNull(), anyString(), anyString(), eq(REGION));
+
+        try (ExecutorService executor = Executors.newFixedThreadPool(2)) {
+            Future<?> transition = executor.submit(() ->
+                    service.setAlarmState("test-alarm", "ALARM", "breached", null, REGION));
+            try {
+                assertTrue(publishing.await(2, TimeUnit.SECONDS));
+                Future<?> unrelated = executor.submit(() -> {
+                    CompositeAlarm composite = new CompositeAlarm();
+                    composite.setAlarmName("unrelated");
+                    composite.setAlarmRule("FALSE");
+                    service.putCompositeAlarm(composite, REGION);
+                    service.setAlarmState("test-alarm", "OK", "recovered", null, REGION);
+                });
+                unrelated.get(2, TimeUnit.SECONDS);
+                assertEquals("OK", alarm.getStateValue());
+            } finally {
+                release.countDown();
+            }
+            transition.get(2, TimeUnit.SECONDS);
+        }
+        ArgumentCaptor<String> messages = ArgumentCaptor.forClass(String.class);
+        verify(sns, times(2)).publish(eq(TOPIC), isNull(), messages.capture(), anyString(), eq(REGION));
+        assertEquals("ALARM", mapper.readTree(messages.getAllValues().getFirst()).path("NewStateValue").asText());
+        assertEquals("OK", mapper.readTree(messages.getAllValues().getLast()).path("NewStateValue").asText());
+    }
+}
@@ -0,0 +1,45 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import io.github.hectorvent.floci.core.common.RegionResolver;
+import io.github.hectorvent.floci.core.storage.InMemoryStorage;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import jakarta.ws.rs.core.MultivaluedHashMap;
+import jakarta.ws.rs.core.MultivaluedMap;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CloudWatchAlarmQueryHandlerTest {
+    @ParameterizedTest
+    @ValueSource(strings = {"PutMetricAlarm", "PutCompositeAlarm"})
+    void sharedFieldsReachBothAlarmTypes(String operation) {
+        String region = "us-east-1";
+        CloudWatchMetricsService service = new CloudWatchMetricsService(new InMemoryStorage<>(),
+                new InMemoryStorage<>(), new RegionResolver(region, "123456789012"));
+        CloudWatchMetricsQueryHandler handler = new CloudWatchMetricsQueryHandler(service, null, null);
+        MultivaluedMap<String, String> request = new MultivaluedHashMap<>();
+        request.putSingle("AlarmName", "shared");
+        request.putSingle("AlarmRule", "FALSE");
+        request.putSingle("AlarmDescription", "shared fields");
+        request.putSingle("ActionsEnabled", "false");
+        request.putSingle("AlarmActions.member.1", "alarm-action");
+        request.putSingle("OKActions.member.1", "ok-action");
+        request.putSingle("InsufficientDataActions.member.1", "missing-action");
+        request.putSingle("Tags.member.1.Key", "team");
+        request.putSingle("Tags.member.1.Value", "metrics");
+        assertEquals(200, handler.handle(operation, request, region).getStatus());
+        Alarm alarm = "PutMetricAlarm".equals(operation)
+                ? service.describeAlarms(List.of("shared"), null, region).getFirst()
+                : service.describeCompositeAlarms(List.of("shared"), null, region).getFirst();
+        assertEquals("shared fields", alarm.getAlarmDescription());
+        assertFalse(alarm.isActionsEnabled());
+        assertEquals(List.of("alarm-action"), alarm.getAlarmActions());
+        assertEquals(List.of("ok-action"), alarm.getOkActions());
+        assertEquals(List.of("missing-action"), alarm.getInsufficientDataActions());
+        assertEquals(Map.of("team", "metrics"), alarm.getTags());
+    }
+}
@@ -0,0 +1,218 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import io.github.hectorvent.floci.core.common.RegionResolver;
+import io.github.hectorvent.floci.core.common.XmlParser;
+import io.github.hectorvent.floci.core.storage.InMemoryStorage;
+import io.github.hectorvent.floci.core.storage.PersistentStorage;
+import io.github.hectorvent.floci.core.storage.StorageBackend;
+import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import jakarta.ws.rs.core.MultivaluedHashMap;
+import jakarta.ws.rs.core.MultivaluedMap;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.w3c.dom.Document;
+
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathFactory;
+import java.nio.file.Path;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+class CloudWatchMetricMathAlarmTest {
+
+    private static final String REGION = "us-east-1";
+    private static final String ALARM_NAME = "metric-math-round-trip";
+    private static final ObjectMapper MAPPER = new ObjectMapper();
+    private static final String XML_ALARM = "/DescribeAlarmsResponse/DescribeAlarmsResult/MetricAlarms/member";
+
+    private CloudWatchMetricsJsonHandler jsonHandler;
+    private CloudWatchMetricsQueryHandler queryHandler;
+
+    @BeforeEach
+    void setup() {
+        initialize(new InMemoryStorage<>());
+    }
+
+    private void initialize(StorageBackend<String, Alarm> alarmStore) {
+        RegionResolver resolver = new RegionResolver(REGION, "000000000000");
+        CloudWatchMetricsService service = new CloudWatchMetricsService(new InMemoryStorage<>(), alarmStore, resolver);
+        CloudWatchDashboardsService dashboards = new CloudWatchDashboardsService(new InMemoryStorage<>(), resolver);
+        jsonHandler = new CloudWatchMetricsJsonHandler(service, dashboards, null, MAPPER);
+        queryHandler = new CloudWatchMetricsQueryHandler(service, dashboards, null);
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void metricMathQueriesRoundTripThroughBothProtocols(boolean queryProtocol) throws Exception {
+        ObjectNode request = metricMathRequest();
+        put(request, queryProtocol);
+        assertMetricMathAlarm(request);
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void metricMathQueriesSurvivePersistentStorageReload(boolean queryProtocol, @TempDir Path directory)
+            throws Exception {
+        Path storageFile = directory.resolve("alarms.json");
+        TypeReference<Map<String, Alarm>> type = new TypeReference<>() { };
+        initialize(new PersistentStorage<>(storageFile, type));
+        ObjectNode request = metricMathRequest();
+        put(request, queryProtocol);
+
+        PersistentStorage<String, Alarm> reloaded = new PersistentStorage<>(storageFile, type);
+        reloaded.load();
+        assertEquals(1, reloaded.keys().size(), "the stored alarm must deserialize after a restart");
+        initialize(reloaded);
+        assertMetricMathAlarm(request);
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void switchingBetweenSingleMetricAndMetricMathReplacesThePreviousDefinition(boolean queryProtocol)
+            throws Exception {
+        ObjectNode singleMetric = singleMetricRequest();
+        put(singleMetric, queryProtocol);
+        assertSingleMetricAlarm(300);
+
+        ObjectNode math = metricMathRequest();
+        put(math, !queryProtocol);
+        assertMetricMathAlarm(math);
+
+        singleMetric.put("Period", 120);
+        put(singleMetric, queryProtocol);
+        assertSingleMetricAlarm(120);
+    }
+
+    @Test
+    void existingSingleMetricDefaultPeriodIsPreserved() throws Exception {
+        ObjectNode singleMetric = singleMetricRequest();
+        singleMetric.remove("Period");
+        put(singleMetric, false);
+        assertSingleMetricAlarm(60);
+    }
+
+    private void put(ObjectNode request, boolean queryProtocol) {
+        if (queryProtocol) {
+            assertEquals(200, queryHandler.handle("PutMetricAlarm", toQuery(request), REGION).getStatus());
+        } else {
+            assertEquals(200, jsonHandler.handle("PutMetricAlarm", request, REGION).getStatus());
+        }
+    }
+
+    private JsonNode describeJson() {
+        ObjectNode request = MAPPER.createObjectNode();
+        request.putArray("AlarmNames").add(ALARM_NAME);
+        JsonNode response = (JsonNode) jsonHandler.handle("DescribeAlarms", request, REGION).getEntity();
+        assertEquals(1, response.path("MetricAlarms").size());
+        return response.path("MetricAlarms").get(0);
+    }
+
+    private Document describeXml() throws Exception {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        params.putSingle("AlarmNames.member.1", ALARM_NAME);
+        String xml = (String) queryHandler.handle("DescribeAlarms", params, REGION).getEntity();
+        return XmlParser.parseDocument(xml);
+    }
+
+    private void assertMetricMathAlarm(ObjectNode request) throws Exception {
+        JsonNode alarm = describeJson();
+        assertEquals(request.path("Metrics"), alarm.path("Metrics"));
+        Document document = describeXml();
+        XPath xpath = XPathFactory.newInstance().newXPath();
+        for (String field : new String[]{"Period", "MetricName", "Namespace", "Statistic", "ExtendedStatistic",
+                "Unit", "Dimensions"}) {
+            assertFalse(alarm.has(field), "metric-math JSON must not contain " + field);
+            assertEquals("0", xpath.evaluate("count(" + XML_ALARM + "/" + field + ")", document),
+                    "metric-math XML must not contain " + field);
+        }
+        assertEquals("3", xpath.evaluate("count(" + XML_ALARM + "/Metrics/member)", document));
+        assertEquals("5", xpath.evaluate(XML_ALARM + "/Threshold", document).replace(".0", ""));
+        assertEquals("2", xpath.evaluate(XML_ALARM + "/EvaluationPeriods", document));
+        assertEquals(5.0, alarm.path("Threshold").asDouble());
+        assertEquals(2, alarm.path("EvaluationPeriods").asInt());
+        assertXmlMatchesJson(request.path("Metrics"), XML_ALARM + "/Metrics", document, xpath);
+    }
+
+    private void assertSingleMetricAlarm(int period) throws Exception {
+        JsonNode alarm = describeJson();
+        assertEquals(period, alarm.path("Period").asInt());
+        assertEquals("AWS/ApiGateway", alarm.path("Namespace").asText());
+        assertEquals("5xx", alarm.path("MetricName").asText());
+        assertEquals("Sum", alarm.path("Statistic").asText());
+        assertFalse(alarm.has("Metrics"));
+        Document document = describeXml();
+        XPath xpath = XPathFactory.newInstance().newXPath();
+        assertEquals(Integer.toString(period), xpath.evaluate(XML_ALARM + "/Period", document));
+        assertEquals("0", xpath.evaluate("count(" + XML_ALARM + "/Metrics)", document));
+    }
+
+    private static void assertXmlMatchesJson(JsonNode value, String path, Document document, XPath xpath)
+            throws Exception {
+        if (value.isArray()) {
+            assertEquals(Integer.toString(value.size()), xpath.evaluate("count(" + path + "/member)", document));
+            for (int index = 0; index < value.size(); index++) {
+                assertXmlMatchesJson(value.get(index), path + "/member[" + (index + 1) + "]", document, xpath);
+            }
+        } else if (value.isObject()) {
+            for (Map.Entry<String, JsonNode> field : value.properties()) {
+                assertXmlMatchesJson(field.getValue(), path + "/" + field.getKey(), document, xpath);
+            }
+        } else {
+            assertEquals(value.asText(), xpath.evaluate(path, document), path);
+        }
+    }
+
+    private static MultivaluedMap<String, String> toQuery(JsonNode value) {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        flatten(value, "", params);
+        return params;
+    }
+
+    private static void flatten(JsonNode value, String prefix, MultivaluedMap<String, String> params) {
+        if (value.isArray()) {
+            for (int index = 0; index < value.size(); index++) {
+                flatten(value.get(index), prefix + ".member." + (index + 1), params);
+            }
+        } else if (value.isObject()) {
+            for (Map.Entry<String, JsonNode> field : value.properties()) {
+                flatten(field.getValue(), prefix.isEmpty() ? field.getKey() : prefix + "." + field.getKey(), params);
+            }
+        } else {
+            params.putSingle(prefix, value.asText());
+        }
+    }
+
+    private static ObjectNode metricMathRequest() throws Exception {
+        return (ObjectNode) MAPPER.readTree("""
+                {"AlarmName":"metric-math-round-trip","EvaluationPeriods":2,"Threshold":5,
+                 "ComparisonOperator":"GreaterThanThreshold","Metrics":[
+                  {"Id":"rate","Expression":"100 * errors / requests","ReturnData":true,
+                   "Period":300,"Label":"Error <rate> & requests"},
+                  {"Id":"errors","ReturnData":false,"AccountId":"123456789012","Label":"Errors",
+                   "MetricStat":{"Metric":{"Namespace":"AWS/ApiGateway","MetricName":"5xx",
+                    "Dimensions":[{"Name":"ApiName","Value":"api<&>"},{"Name":"Stage","Value":"test"}]},
+                    "Period":300,"Stat":"Sum","Unit":"Count"}},
+                  {"Id":"requests","ReturnData":false,"MetricStat":{
+                   "Metric":{"Namespace":"AWS/ApiGateway","MetricName":"Count"},"Period":300,"Stat":"Sum"}}
+                 ]}
+                """);
+    }
+
+    private static ObjectNode singleMetricRequest() throws Exception {
+        return (ObjectNode) MAPPER.readTree("""
+                {"AlarmName":"metric-math-round-trip","Namespace":"AWS/ApiGateway","MetricName":"5xx",
+                 "Statistic":"Sum","Period":300,"EvaluationPeriods":2,"Threshold":5,
+                 "ComparisonOperator":"GreaterThanThreshold"}
+                """);
+    }
+}
@@ -0,0 +1,203 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.RestAssured;
+import io.restassured.config.EncoderConfig;
+import io.restassured.http.ContentType;
+import io.restassured.parsing.Parser;
+import io.restassured.specification.RequestSpecification;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+
+import static io.restassured.RestAssured.config;
+import static io.restassured.RestAssured.given;
+import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasItem;
+
+/**
+ * PutMetricData datums nested under EntityMetricData, as the CloudWatch Agent sends them,
+ * must be stored under the request namespace on every protocol path. floci-io/floci#6066.
+ */
+@QuarkusTest
+class CloudWatchMetricsEntityMetricDataIntegrationTest {
+
+    private static final String CW_AUTH =
+            "AWS4-HMAC-SHA256 Credential=test/20261020/us-east-1/monitoring/aws4_request";
+    private static final String JSON_1_0 = "application/x-amz-json-1.0";
+
+    @BeforeAll
+    static void registerJsonParser() {
+        RestAssured.registerParser(JSON_1_0, Parser.JSON);
+    }
+
+    private static RequestSpecification json(String operation) {
+        return given()
+                .header("Authorization", CW_AUTH)
+                .contentType(JSON_1_0)
+                .config(config().encoderConfig(EncoderConfig.encoderConfig()
+                        .encodeContentTypeAs(JSON_1_0, ContentType.TEXT)))
+                .header("X-Amz-Target", "GraniteServiceVersion20100801." + operation);
+    }
+
+    private static RequestSpecification query(String action) {
+        return given()
+                .header("Authorization", CW_AUTH)
+                .contentType("application/x-www-form-urlencoded")
+                .formParam("Action", action)
+                .formParam("Version", "2010-08-01");
+    }
+
+    @Test
+    void jsonEntityMetricDataOnlyIsListedAndAggregated() {
+        long now = Instant.now().getEpochSecond();
+        json("PutMetricData")
+                .body("""
+                        {"Namespace":"CWAgent/Json","MetricData":[],
+                         "EntityMetricData":[{
+                           "Entity":{"KeyAttributes":{"Type":"AWS::Resource",
+                             "ResourceType":"AWS::EC2::Instance","Identifier":"i-0123456789abcdef0"},
+                             "Attributes":{}},
+                           "MetricData":[
+                             {"MetricName":"mem_used_percent","Value":6.5,"Unit":"Percent",
+                              "StorageResolution":60,"Timestamp":%d,
+                              "Dimensions":[{"Name":"host","Value":"h1"}]},
+                             {"MetricName":"disk_used_percent","Value":0.75,"Unit":"Percent",
+                              "StorageResolution":60,"Timestamp":%d,
+                              "Dimensions":[{"Name":"host","Value":"h1"}]}]}],
+                         "StrictEntityValidation":false}
+                        """.formatted(now, now))
+        .when().post("/")
+        .then().statusCode(200);
+
+        json("ListMetrics")
+                .body("{\"Namespace\":\"CWAgent/Json\"}")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("Metrics.MetricName", containsInAnyOrder("mem_used_percent", "disk_used_percent"));
+
+        json("GetMetricStatistics")
+                .body("""
+                        {"Namespace":"CWAgent/Json","MetricName":"mem_used_percent",
+                         "Dimensions":[{"Name":"host","Value":"h1"}],
+                         "StartTime":%d,"EndTime":%d,"Period":60,"Statistics":["Sum"]}
+                        """.formatted(now - 120, now + 120))
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("Datapoints.Sum", hasItem(6.5f));
+    }
+
+    @Test
+    void jsonTopLevelAndEntityMetricDataAreBothStored() {
+        json("PutMetricData")
+                .body("""
+                        {"Namespace":"CWAgent/JsonMixed",
+                         "MetricData":[{"MetricName":"TopLevel","Value":1}],
+                         "EntityMetricData":[{"Entity":{"KeyAttributes":{"Type":"Service",
+                           "Name":"checkout","Environment":"prod"}},
+                           "MetricData":[{"MetricName":"FromEntity","Value":2}]}]}
+                        """)
+        .when().post("/")
+        .then().statusCode(200);
+
+        json("ListMetrics")
+                .body("{\"Namespace\":\"CWAgent/JsonMixed\"}")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("Metrics.MetricName", containsInAnyOrder("TopLevel", "FromEntity"));
+    }
+
+    @Test
+    void queryTopLevelAndEntityMetricDataAreListedAndAggregated() {
+        Instant now = Instant.now();
+        query("PutMetricData")
+                .formParam("Namespace", "CWAgent/Query")
+                .formParam("MetricData.member.1.MetricName", "TopLevel")
+                .formParam("MetricData.member.1.Value", "1")
+                .formParam("EntityMetricData.member.1.Entity.KeyAttributes.entry.1.key", "Type")
+                .formParam("EntityMetricData.member.1.Entity.KeyAttributes.entry.1.value", "AWS::Resource")
+                .formParam("EntityMetricData.member.1.MetricData.member.1.MetricName", "mem_used_percent")
+                .formParam("EntityMetricData.member.1.MetricData.member.1.Value", "6.5")
+                .formParam("EntityMetricData.member.1.MetricData.member.1.Timestamp", now.toString())
+                .formParam("EntityMetricData.member.1.MetricData.member.1.Dimensions.member.1.Name", "host")
+                .formParam("EntityMetricData.member.1.MetricData.member.1.Dimensions.member.1.Value", "h1")
+                .formParam("StrictEntityValidation", "false")
+        .when().post("/")
+        .then().statusCode(200);
+
+        query("ListMetrics")
+                .formParam("Namespace", "CWAgent/Query")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("ListMetricsResponse.ListMetricsResult.Metrics.member.MetricName",
+                        containsInAnyOrder("TopLevel", "mem_used_percent"));
+
+        query("GetMetricStatistics")
+                .formParam("Namespace", "CWAgent/Query")
+                .formParam("MetricName", "mem_used_percent")
+                .formParam("Dimensions.member.1.Name", "host")
+                .formParam("Dimensions.member.1.Value", "h1")
+                .formParam("StartTime", now.minusSeconds(120).toString())
+                .formParam("EndTime", now.plusSeconds(120).toString())
+                .formParam("Period", "60")
+                .formParam("Statistics.member.1", "Sum")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("GetMetricStatisticsResponse.GetMetricStatisticsResult.Datapoints.member.Sum",
+                        equalTo("6.5"));
+    }
+
+    @Test
+    void jsonNestedDatumWithoutMetricNameIsRejectedAndNothingIsStored() {
+        json("PutMetricData")
+                .body("""
+                        {"Namespace":"CWAgent/JsonInvalid",
+                         "MetricData":[{"MetricName":"TopLevel","Value":1}],
+                         "EntityMetricData":[{"MetricData":[{"Value":2}]}]}
+                        """)
+        .when().post("/")
+        .then()
+                .statusCode(400)
+                .header("x-amzn-query-error", equalTo("MissingParameter;Sender"))
+                .body("__type", equalTo("MissingRequiredParameterException"))
+                .body("message", equalTo(
+                        "The parameter EntityMetricData.member.1.MetricData.member.1.MetricName is required."));
+
+        json("ListMetrics")
+                .body("{\"Namespace\":\"CWAgent/JsonInvalid\"}")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("Metrics", empty());
+    }
+
+    @Test
+    void queryMemberWithoutMetricNameIsRejectedAndNothingIsStored() {
+        query("PutMetricData")
+                .formParam("Namespace", "CWAgent/QueryInvalid")
+                .formParam("MetricData.member.1.Value", "1")
+                .formParam("MetricData.member.2.MetricName", "Valid")
+                .formParam("MetricData.member.2.Value", "2")
+        .when().post("/")
+        .then()
+                .statusCode(400)
+                .body("ErrorResponse.Error.Code", equalTo("MissingParameter"))
+                .body("ErrorResponse.Error.Message",
+                        equalTo("The parameter MetricData.member.1.MetricName is required."));
+
+        query("ListMetrics")
+                .formParam("Namespace", "CWAgent/QueryInvalid")
+        .when().post("/")
+        .then()
+                .statusCode(200)
+                .body("ListMetricsResponse.ListMetricsResult.Metrics.member.size()", equalTo(0));
+    }
+}
@@ -8,6 +8,7 @@ import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
+import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.core.common.RegionResolver;
 import io.github.hectorvent.floci.core.storage.InMemoryStorage;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
@@ -17,6 +18,13 @@ import java.math.BigDecimal;
 import java.time.Instant;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;

 /**
 * Handler-level tests for CloudWatchMetricsJsonHandler.
@@ -146,6 +154,114 @@ class CloudWatchMetricsJsonHandlerTest {
                "metric stored with 24h-ago timestamp must not appear in a 20-second window around now");
    }

+    // The CloudWatch Agent sends an empty top-level MetricData and nests every datum under
+    // EntityMetricData, floci-io/floci#6066.
+    @Test
+    void putMetricData_entityMetricDataOnly_storesNestedDatumsUnderTheRequestNamespace() {
+        ObjectNode req = MAPPER.createObjectNode();
+        req.put("Namespace", "CWAgent");
+        req.putArray("MetricData");
+        ObjectNode entityMetricData = req.putArray("EntityMetricData").addObject();
+        ObjectNode entity = entityMetricData.putObject("Entity");
+        entity.putObject("KeyAttributes")
+                .put("Type", "AWS::Resource")
+                .put("ResourceType", "AWS::EC2::Instance")
+                .put("Identifier", "i-0123456789abcdef0");
+        entity.putObject("Attributes");
+        ObjectNode datum = entityMetricData.putArray("MetricData").addObject();
+        datum.put("MetricName", "mem_used_percent");
+        datum.put("Value", 6.43);
+        datum.put("Unit", "Percent");
+        datum.put("StorageResolution", 60);
+        datum.put("Timestamp", sdkTimestamp(EPOCH_NOW));
+        datum.putArray("Dimensions").addObject().put("Name", "host").put("Value", "h1");
+        req.put("StrictEntityValidation", false);
+
+        assertEquals(200, handler.handle("PutMetricData", req, REGION).getStatus());
+
+        ObjectNode stats = getStats("CWAgent", "mem_used_percent", "host", "h1",
+                EPOCH_NOW.minusSeconds(60), EPOCH_NOW.plusSeconds(60), 60);
+        assertEquals(1, stats.get("Datapoints").size());
+        assertEquals(6.43, stats.get("Datapoints").get(0).get("Sum").asDouble());
+    }
+
+    @Test
+    void putMetricData_topLevelAndEntityMetricData_storesBoth() {
+        ObjectNode req = MAPPER.createObjectNode();
+        req.put("Namespace", "Mixed");
+        req.putArray("MetricData").addObject()
+                .put("MetricName", "TopLevel").put("Value", 1.0);
+        ArrayNode entityMetricData = req.putArray("EntityMetricData");
+        entityMetricData.addObject().putArray("MetricData").addObject()
+                .put("MetricName", "FirstEntity").put("Value", 2.0);
+        entityMetricData.addObject().putArray("MetricData").addObject()
+                .put("MetricName", "SecondEntity").put("Value", 3.0);
+
+        assertEquals(200, handler.handle("PutMetricData", req, REGION).getStatus());
+
+        ObjectNode listReq = MAPPER.createObjectNode();
+        listReq.put("Namespace", "Mixed");
+        ObjectNode listed = (ObjectNode) handler.handle("ListMetrics", listReq, REGION).getEntity();
+        List<String> names = new ArrayList<>();
+        listed.get("Metrics").forEach(m -> names.add(m.get("MetricName").asText()));
+        assertEquals(List.of("FirstEntity", "SecondEntity", "TopLevel"), names.stream().sorted().toList());
+    }
+
+    @Test
+    void putMetricData_entityDatumWithoutMetricName_rejectsTheWholeRequest() {
+        ObjectNode req = MAPPER.createObjectNode();
+        req.put("Namespace", "Invalid");
+        req.putArray("MetricData").addObject()
+                .put("MetricName", "TopLevel").put("Value", 1.0);
+        ArrayNode nested = req.putArray("EntityMetricData").addObject().putArray("MetricData");
+        nested.addObject().put("MetricName", "Valid").put("Value", 2.0);
+        nested.addObject().put("Value", 3.0);
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> handler.handle("PutMetricData", req, REGION));
+        assertEquals("MissingParameter", e.getErrorCode());
+        assertEquals("MissingRequiredParameterException", e.jsonType());
+        assertEquals(400, e.getHttpStatus());
+        assertEquals("The parameter EntityMetricData.member.1.MetricData.member.2.MetricName is required.",
+                e.getMessage());
+        assertEquals(0, listMetricNames("Invalid").size());
+    }
+
+    @Test
+    void putMetricData_topLevelDatumWithEmptyMetricName_rejectsTheWholeRequest() {
+        ObjectNode req = MAPPER.createObjectNode();
+        req.put("Namespace", "InvalidTop");
+        ArrayNode data = req.putArray("MetricData");
+        data.addObject().put("MetricName", "Valid").put("Value", 1.0);
+        data.addObject().put("MetricName", "").put("Value", 2.0);
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> handler.handle("PutMetricData", req, REGION));
+        assertEquals("MissingParameter", e.getErrorCode());
+        assertEquals("The parameter MetricData.member.2.MetricName is required.", e.getMessage());
+        assertEquals(0, listMetricNames("InvalidTop").size());
+    }
+
+    // AWS constrains MetricName to 1 to 255 characters with no pattern, so whitespace is a name.
+    @Test
+    void putMetricData_whitespaceMetricName_isStored() {
+        ObjectNode req = MAPPER.createObjectNode();
+        req.put("Namespace", "WhitespaceName");
+        req.putArray("MetricData").addObject().put("MetricName", " ").put("Value", 1.0);
+
+        assertEquals(200, handler.handle("PutMetricData", req, REGION).getStatus());
+        assertEquals(List.of(" "), listMetricNames("WhitespaceName"));
+    }
+
+    private List<String> listMetricNames(String namespace) {
+        ObjectNode listReq = MAPPER.createObjectNode();
+        listReq.put("Namespace", namespace);
+        ObjectNode listed = (ObjectNode) handler.handle("ListMetrics", listReq, REGION).getEntity();
+        List<String> names = new ArrayList<>();
+        listed.get("Metrics").forEach(m -> names.add(m.get("MetricName").asText()));
+        return names;
+    }
+
    @Test
    void setAlarmState_updatesFieldsCorrectly() {
        putMetric("NS", "M", "type", "current", 100.0, EPOCH_NOW);
@@ -234,6 +350,22 @@ class CloudWatchMetricsJsonHandlerTest {
        assertEquals("Count", alarm.get("Unit").asText());
    }

+    // AWS sends every alarm collection even when it is empty. The CLI's text output writes a
+    // None line for each paginator result key missing from the page (floci-io/floci#6362).
+    @Test
+    void describeAlarms_returnsEmptyCompositeAndLogAlarmCollections() {
+        handler.handle("PutMetricAlarm", alarmRequest("MetricOnly"), REGION);
+
+        ObjectNode response = (ObjectNode) handler.handle("DescribeAlarms", MAPPER.createObjectNode(), REGION)
+                .getEntity();
+
+        assertEquals(1, response.get("MetricAlarms").size());
+        assertTrue(response.get("CompositeAlarms").isArray());
+        assertTrue(response.get("CompositeAlarms").isEmpty());
+        assertTrue(response.get("LogAlarms").isArray());
+        assertTrue(response.get("LogAlarms").isEmpty());
+    }
+
    // An alarm the caller never gave an M for reports no DatapointsToAlarm at all. AWS omits the
    // member in that case, and echoing EvaluationPeriods instead reads as a change to any client
    // that re-plans against its own configuration, which is what floci-io/floci#3660 hit.
@@ -1,6 +1,9 @@
 package io.github.hectorvent.floci.services.cloudwatch.metrics;

+import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricDatum;
 import io.github.hectorvent.floci.services.cloudwatch.metricstreams.CloudWatchMetricStreamsService;
 import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
 import jakarta.ws.rs.core.MultivaluedHashMap;
@@ -12,12 +15,15 @@ import java.util.List;

 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;

@@ -123,4 +129,128 @@ class CloudWatchMetricsQueryHandlerTest {
                anyInt(), any(), unitCaptor.capture(), any());
        assertEquals("Count", unitCaptor.getValue());
    }
+
+    // The Query serialization of EntityMetricData nests each datum two lists deep;
+    // floci-io/floci#6066 is the JSON-side report of the same dropped datums.
+    @Test
+    void putMetricDataStoresTopLevelAndEntityMetricDataUnderTheRequestNamespace() {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        params.putSingle("Namespace", "CWAgent");
+        params.putSingle("MetricData.member.1.MetricName", "TopLevel");
+        params.putSingle("MetricData.member.1.Value", "1");
+        params.putSingle("EntityMetricData.member.1.Entity.KeyAttributes.entry.1.key", "Type");
+        params.putSingle("EntityMetricData.member.1.Entity.KeyAttributes.entry.1.value", "AWS::Resource");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.MetricName", "mem_used_percent");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.Value", "6.5");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.Unit", "Percent");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.Dimensions.member.1.Name", "host");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.Dimensions.member.1.Value", "h1");
+        params.putSingle("EntityMetricData.member.2.MetricData.member.1.MetricName", "disk_used_percent");
+        params.putSingle("EntityMetricData.member.2.MetricData.member.1.Value", "0.75");
+        params.putSingle("StrictEntityValidation", "false");
+
+        handler.handle("PutMetricData", params, REGION);
+
+        @SuppressWarnings("unchecked")
+        ArgumentCaptor<List<MetricDatum>> captor = ArgumentCaptor.forClass(List.class);
+        verify(metricsService).putMetricData(eq("CWAgent"), captor.capture(), eq(REGION));
+        List<MetricDatum> datums = captor.getValue();
+        assertEquals(List.of("TopLevel", "mem_used_percent", "disk_used_percent"),
+                datums.stream().map(MetricDatum::getMetricName).toList());
+        MetricDatum entityDatum = datums.get(1);
+        assertEquals(6.5, entityDatum.getValue());
+        assertEquals("Percent", entityDatum.getUnit());
+        assertEquals("host", entityDatum.getDimensions().get(0).name());
+        assertEquals("h1", entityDatum.getDimensions().get(0).value());
+    }
+
+    @Test
+    void putMetricDataStoresEntityMetricDataAfterAnEmptyEntityEntry() {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        params.putSingle("Namespace", "CWAgent");
+        params.putSingle("EntityMetricData.member.2.MetricData.member.1.MetricName", "M");
+        params.putSingle("EntityMetricData.member.2.MetricData.member.1.Value", "1");
+        params.putSingle("EntityMetricData.member.10.MetricData.member.1.MetricName", "N");
+        params.putSingle("EntityMetricData.member.10.MetricData.member.1.Value", "2");
+        params.putSingle("StrictEntityValidation", "false");
+
+        handler.handle("PutMetricData", params, REGION);
+
+        @SuppressWarnings("unchecked")
+        ArgumentCaptor<List<MetricDatum>> captor = ArgumentCaptor.forClass(List.class);
+        verify(metricsService).putMetricData(eq("CWAgent"), captor.capture(), eq(REGION));
+        List<MetricDatum> datums = captor.getValue();
+        assertEquals(List.of("M", "N"), datums.stream().map(MetricDatum::getMetricName).toList());
+        assertEquals(1.0, datums.get(0).getValue());
+        assertEquals(2.0, datums.get(1).getValue());
+    }
+
+    @Test
+    void putMetricDataRejectsAMemberWithoutMetricNameBeforeStoringAnything() {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        params.putSingle("Namespace", "NS");
+        params.putSingle("MetricData.member.1.Value", "1");
+        params.putSingle("MetricData.member.2.MetricName", "Valid");
+        params.putSingle("MetricData.member.2.Value", "2");
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> handler.handle("PutMetricData", params, REGION));
+        assertEquals("MissingParameter", e.getErrorCode());
+        assertEquals("MissingRequiredParameterException", e.jsonType());
+        assertEquals(400, e.getHttpStatus());
+        assertEquals("The parameter MetricData.member.1.MetricName is required.", e.getMessage());
+        verify(metricsService, never()).putMetricData(any(), any(), any());
+    }
+
+    @Test
+    void putMetricDataRejectsANestedMemberWithoutMetricNameBeforeStoringAnything() {
+        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
+        params.putSingle("Namespace", "NS");
+        params.putSingle("MetricData.member.1.MetricName", "TopLevel");
+        params.putSingle("MetricData.member.1.Value", "1");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.1.Unit", "Percent");
+        params.putSingle("EntityMetricData.member.1.MetricData.member.2.MetricName", "Valid");
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> handler.handle("PutMetricData", params, REGION));
+        assertEquals("The parameter EntityMetricData.member.1.MetricData.member.1.MetricName is required.",
+                e.getMessage());
+        verify(metricsService, never()).putMetricData(any(), any(), any());
+    }
+
+    @Test
+    void putMetricDataRejectsAnEmptyMetricNameButAcceptsWhitespace() {
+        MultivaluedMap<String, String> empty = new MultivaluedHashMap<>();
+        empty.putSingle("Namespace", "NS");
+        empty.putSingle("MetricData.member.1.MetricName", "");
+        empty.putSingle("MetricData.member.1.Value", "1");
+
+        AwsException e = assertThrows(AwsException.class,
+                () -> handler.handle("PutMetricData", empty, REGION));
+        assertEquals("The parameter MetricData.member.1.MetricName is required.", e.getMessage());
+        verify(metricsService, never()).putMetricData(any(), any(), any());
+
+        MultivaluedMap<String, String> whitespace = new MultivaluedHashMap<>();
+        whitespace.putSingle("Namespace", "NS");
+        whitespace.putSingle("MetricData.member.1.MetricName", " ");
+        whitespace.putSingle("MetricData.member.1.Value", "1");
+
+        handler.handle("PutMetricData", whitespace, REGION);
+
+        @SuppressWarnings("unchecked")
+        ArgumentCaptor<List<MetricDatum>> captor = ArgumentCaptor.forClass(List.class);
+        verify(metricsService).putMetricData(eq("NS"), captor.capture(), eq(REGION));
+        assertEquals(List.of(" "), captor.getValue().stream().map(MetricDatum::getMetricName).toList());
+    }
+
+    @Test
+    void describeAlarmsReturnsEmptyCompositeAndLogAlarmCollections() {
+        when(metricsService.describeAlarms(any(), any(), eq(REGION))).thenReturn(List.of());
+
+        String xml = (String) handler.handle("DescribeAlarms", new MultivaluedHashMap<>(), REGION).getEntity();
+
+        assertTrue(xml.contains("<MetricAlarms></MetricAlarms>"), xml);
+        assertTrue(xml.contains("<CompositeAlarms></CompositeAlarms>"), xml);
+        assertTrue(xml.contains("<LogAlarms></LogAlarms>"), xml);
+    }
 }
@@ -2,6 +2,7 @@ package io.github.hectorvent.floci.services.cloudwatch.metrics;

 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.core.common.AwsException;
 import io.github.hectorvent.floci.core.common.RegionResolver;
 import io.github.hectorvent.floci.core.storage.InMemoryStorage;
 import io.github.hectorvent.floci.services.cloudwatch.dashboards.CloudWatchDashboardsService;
@@ -83,6 +84,34 @@ class CloudWatchMetricsTagsTest {
        assertNull(tags.get("team"));
    }

+    /**
+     * An ARN naming no alarm is an error on all three operations, not a silent no-op. The ARN
+     * used here differs from a working one only in the alarm name, so the outcome cannot be
+     * explained by the ARN failing to parse.
+     */
+    @Test
+    void tagOperationsRejectAnArnThatNamesNoAlarm() {
+        MetricAlarm alarm = new MetricAlarm();
+        alarm.setAlarmName("test-alarm");
+        alarm.setAlarmArn("arn:aws:cloudwatch:us-east-1:000000000000:alarm:test-alarm");
+        service.putMetricAlarm(alarm, REGION);
+        String ghost = "arn:aws:cloudwatch:us-east-1:000000000000:alarm:nosuch";
+
+        for (Runnable call : List.<Runnable>of(
+                () -> service.tagResource(ghost, Map.of("env", "prod"), REGION),
+                () -> service.untagResource(ghost, List.of("env"), REGION),
+                () -> service.listTagsForResource(ghost, REGION))) {
+            AwsException e = assertThrows(AwsException.class, call::run);
+            assertEquals("ResourceNotFoundException", e.getErrorCode());
+            assertEquals(404, e.getHttpStatus());
+        }
+
+        // The failures wrote nothing: the real alarm still carries only what it was given.
+        assertEquals(Map.of(), service.listTagsForResource(alarm.getAlarmArn(), REGION));
+        service.tagResource(alarm.getAlarmArn(), Map.of("env", "dev"), REGION);
+        assertEquals(Map.of("env", "dev"), service.listTagsForResource(alarm.getAlarmArn(), REGION));
+    }
+
    @Test
    void tagsViaPutMetricAlarmQuery() {
        MultivaluedMap<String, String> params = new MultivaluedHashMap<>();
@@ -0,0 +1,160 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.testing.PartitionCleanup;
+import io.github.hectorvent.floci.testing.RestAssuredJsonUtils;
+import io.quarkus.test.common.http.TestHTTPResource;
+import io.quarkus.test.junit.QuarkusTest;
+import io.restassured.response.Response;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.net.URI;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import static io.restassured.RestAssured.given;
+import static org.junit.jupiter.api.Assertions.*;
+
+@QuarkusTest
+class CompositeAlarmIntegrationTest {
+    private static final ObjectMapper MAPPER = new ObjectMapper();
+    private static final String SCOPE =
+            "AWS4-HMAC-SHA256 Credential=test/20261010/cn-north-1/monitoring/aws4_request";
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @RegisterExtension
+    final PartitionCleanup cleanup = new PartitionCleanup();
+
+    @BeforeAll
+    static void configureRestAssured() {
+        RestAssuredJsonUtils.configureAwsContentTypes();
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void bothProtocolsCreateDescribeEvaluateAndDeleteRealAlarms(boolean json) throws Exception {
+        String prefix = "wire-composite-" + Long.toString(System.nanoTime(), 36);
+        String source = prefix + "-source";
+        String aggregate = prefix + "-aggregate";
+        call(json, "PutCompositeAlarm", Map.of("AlarmName", source, "AlarmRule", "TRUE")).then().statusCode(200);
+        call(json, "PutCompositeAlarm", Map.of("AlarmName", aggregate, "AlarmRule", "ALARM(\"" + source + "\")",
+                "ActionsEnabled", false, "AlarmDescription", "combined")).then().statusCode(200);
+        Response result = call(json, "DescribeAlarms", Map.of("AlarmNames", List.of(aggregate),
+                "AlarmTypes", List.of("CompositeAlarm")));
+        result.then().statusCode(200);
+        if (json) {
+            assertEquals(List.of(), result.jsonPath().getList("LogAlarms"));
+            assertEquals(1, result.jsonPath().getList("CompositeAlarms").size());
+            assertEquals("ALARM", result.jsonPath().getString("CompositeAlarms[0].StateValue"));
+            assertEquals("arn:aws-cn:cloudwatch:cn-north-1:000000000000:alarm:" + aggregate,
+                    result.jsonPath().getString("CompositeAlarms[0].AlarmArn"));
+            assertFalse(result.jsonPath().getBoolean("CompositeAlarms[0].ActionsEnabled"));
+        } else {
+            assertTrue(result.asString().contains("<LogAlarms>"));
+            assertEquals("ALARM", result.xmlPath().getString(
+                    "DescribeAlarmsResponse.DescribeAlarmsResult.CompositeAlarms.member.StateValue"));
+            assertTrue(result.asString().contains("arn:aws-cn:cloudwatch:cn-north-1:000000000000:alarm:" + aggregate));
+            assertEquals("false", result.xmlPath().getString(
+                    "DescribeAlarmsResponse.DescribeAlarmsResult.CompositeAlarms.member.ActionsEnabled"));
+        }
+        assertFalse(call(json, "DescribeAlarms", Map.of("AlarmNames", List.of(aggregate)))
+                .then().statusCode(200).extract().asString().contains(aggregate));
+        call(json, "SetAlarmState", Map.of("AlarmName", source, "StateValue", "OK",
+                "StateReason", "recovery")).then().statusCode(200);
+        Response recovered = call(json, "DescribeAlarms", Map.of("AlarmNames", List.of(aggregate),
+                "AlarmTypes", List.of("CompositeAlarm")));
+        assertEquals("OK", json ? recovered.jsonPath().getString("CompositeAlarms[0].StateValue")
+                : recovered.xmlPath().getString(
+                        "DescribeAlarmsResponse.DescribeAlarmsResult.CompositeAlarms.member.StateValue"));
+        for (String name : List.of(aggregate, source)) {
+            call(json, "DeleteAlarms", Map.of("AlarmNames", List.of(name))).then().statusCode(200);
+        }
+        Response empty = call(json, "DescribeAlarms", Map.of("AlarmNamePrefix", prefix,
+                "AlarmTypes", List.of("CompositeAlarm")));
+        assertFalse(empty.asString().contains(aggregate));
+        assertFalse(empty.asString().contains(source));
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void invalidRuleAndUnsupportedSuppressionCannotCreateAnAlarm(boolean json) throws Exception {
+        String name = "invalid-composite-" + Long.toString(System.nanoTime(), 36);
+        call(json, "PutCompositeAlarm", Map.of("AlarmName", name, "AlarmRule", "TRUE AND"))
+                .then().statusCode(400);
+        call(json, "PutCompositeAlarm", Map.of("AlarmName", name, "AlarmRule", "TRUE",
+                "ActionsSuppressor", "other")).then().statusCode(400);
+        assertFalse(call(json, "DescribeAlarms", Map.of("AlarmNames", List.of(name),
+                "AlarmTypes", List.of("CompositeAlarm"))).asString().contains(name));
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void alarmTypeValidationAcceptsLogAlarmsAndUsesSmithyErrors(boolean json) throws Exception {
+        call(json, "DescribeAlarms", Map.of("AlarmTypes", List.of("LogAlarm"))).then().statusCode(200);
+        Response error = call(json, "DescribeAlarms", Map.of("AlarmTypes", List.of("Unknown")));
+        error.then().statusCode(400);
+        assertEquals("1 validation error detected: Value '[Unknown]' at 'alarmTypes' failed to satisfy constraint: "
+                + "Member must satisfy constraint: [Member must satisfy enum value set: "
+                + "[CompositeAlarm, MetricAlarm, LogAlarm]]", errorMessage(json, error));
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void lengthErrorsUseSmithyMessages(boolean json) throws Exception {
+        for (String field : List.of("AlarmName", "AlarmRule")) {
+            int maximum = "AlarmName".equals(field) ? 255 : 10240;
+            String path = "AlarmName".equals(field) ? "alarmName" : "alarmRule";
+            for (String value : List.of("", "x".repeat(maximum + 1))) {
+                Map<String, String> request = new LinkedHashMap<>(Map.of("AlarmName", "length-validation", "AlarmRule", "TRUE"));
+                request.put(field, value);
+                Response error = call(json, "PutCompositeAlarm", request);
+                error.then().statusCode(400);
+                assertEquals("1 validation error detected: Value '" + value + "' at '" + path
+                        + "' failed to satisfy constraint: Member must have length "
+                        + (value.isEmpty() ? "greater than or equal to 1" : "less than or equal to " + maximum),
+                        errorMessage(json, error));
+            }
+        }
+    }
+
+    private String errorMessage(boolean json, Response response) {
+        return json ? response.jsonPath().getString("message") : response.xmlPath().getString("ErrorResponse.Error.Message");
+    }
+
+    private Response call(boolean json, String operation, Map<String, ?> body)
+            throws JsonProcessingException {
+        if ("PutCompositeAlarm".equals(operation)) {
+            String name = body.get("AlarmName").toString();
+            cleanup.register(() -> given().port(baseUri.getPort()).contentType("application/x-amz-json-1.0")
+                    .header("Authorization", SCOPE)
+                    .header("X-Amz-Target", "GraniteServiceVersion20100801.DeleteAlarms")
+                    .body(MAPPER.valueToTree(Map.of("AlarmNames", List.of(name))).toString())
+                    .post("/").then().statusCode(200));
+        }
+        if (json) {
+            return given().contentType("application/x-amz-json-1.0").header("Authorization", SCOPE)
+                    .header("X-Amz-Target", "GraniteServiceVersion20100801." + operation)
+                    .body(MAPPER.writeValueAsString(body)).post("/");
+        }
+        Map<String, Object> form = new LinkedHashMap<>();
+        form.put("Action", operation);
+        body.forEach((key, value) -> {
+            if (value instanceof List<?> values) {
+                for (int index = 0; index < values.size(); index++) {
+                    form.put(key + ".member." + (index + 1), values.get(index));
+                }
+            } else {
+                form.put(key, value);
+            }
+        });
+        return given().contentType("application/x-www-form-urlencoded").header("Authorization", SCOPE)
+                .formParams(form).post("/");
+    }
+}
@@ -0,0 +1,274 @@
+package io.github.hectorvent.floci.services.cloudwatch.metrics;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.github.hectorvent.floci.core.common.AwsException;
+import io.github.hectorvent.floci.core.common.RegionResolver;
+import io.github.hectorvent.floci.core.storage.InMemoryStorage;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.Alarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.CompositeAlarm;
+import io.github.hectorvent.floci.services.cloudwatch.metrics.model.MetricAlarm;
+import io.github.hectorvent.floci.testing.ThreadStates;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CompositeAlarmServiceTest {
+    private static final String REGION = "cn-north-1";
+    private final CloudWatchMetricsService service = new CloudWatchMetricsService(
+            new InMemoryStorage<>(), new InMemoryStorage<>(), new RegionResolver(REGION, "123456789012"));
+
+    @Test
+    void metricTransitionsPropagateThroughNamesArnsAndNestedComposites() {
+        MetricAlarm metric = new MetricAlarm();
+        metric.setAlarmName("latency");
+        service.putMetricAlarm(metric, REGION);
+        put("combined", "ALARM(\"" + metric.getAlarmArn() + "\") AND NOT ALARM(\"maintenance\")");
+        put("outer", "ALARM(combined) OR (TRUE AND FALSE)");
+        assertEquals("OK", state("outer"));
+        service.setAlarmState("latency", "ALARM", "high latency", null, REGION);
+        assertEquals("ALARM", state("combined"));
+        assertEquals("ALARM", state("outer"));
+        service.setAlarmState("latency", "OK", "recovered", null, REGION);
+        assertEquals("OK", state("outer"));
+        assertEquals(List.of(metric), service.describeAlarms(null, null, REGION));
+        assertTrue(service.describeCompositeAlarms(null, null, "us-east-1").isEmpty());
+        assertTrue(service.describeCompositeAlarms(List.of("combined"), null, REGION)
+                .getFirst().getAlarmArn().startsWith("arn:aws-cn:cloudwatch:"));
+    }
+
+    @Test
+    void updatesPreserveStateAndTagsUntilTheNextDependencyChange() {
+        put("source", "FALSE");
+        CompositeAlarm alarm = put("aggregate", "ALARM(source)");
+        service.tagResource(alarm.getAlarmArn(), Map.of("owner", "retained"), REGION);
+        service.setAlarmState("aggregate", "ALARM", "manual", null, REGION);
+        CompositeAlarm replacement = put("aggregate", "OK(source)");
+        assertEquals("ALARM", replacement.getStateValue());
+        assertEquals(Map.of("owner", "retained"), replacement.getTags());
+        service.setAlarmState("source", "ALARM", "dependency changed", null, REGION);
+        assertEquals("OK", state("aggregate"));
+    }
+
+    @Test
+    void unrelatedWritesPreserveManualCompositeStatesAndParentStates() {
+        put("source", "FALSE");
+        put("aggregate", "ALARM(source)");
+        put("parent", "ALARM(aggregate)");
+        service.setAlarmState("aggregate", "ALARM", "manual", null, REGION);
+        assertEquals("ALARM", state("parent"));
+        put("unrelated", "TRUE");
+        assertEquals("ALARM", state("aggregate"));
+        assertEquals("ALARM", state("parent"));
+        MetricAlarm metric = new MetricAlarm();
+        metric.setAlarmName("unrelated-metric");
+        service.putMetricAlarm(metric, REGION);
+        assertEquals("ALARM", state("aggregate"));
+        service.setAlarmState("unrelated-metric", "ALARM", "unrelated", null, REGION);
+        assertEquals("ALARM", state("aggregate"));
+        service.deleteAlarms(List.of("unrelated"), REGION);
+        assertEquals("ALARM", state("aggregate"));
+        assertEquals("ALARM", state("parent"));
+        service.setAlarmState("source", "ALARM", "child changed", null, REGION);
+        service.setAlarmState("source", "OK", "child recovered", null, REGION);
+        assertEquals("OK", state("aggregate"));
+        assertEquals("OK", state("parent"));
+    }
+
+    @Test
+    void unchangedChildStateDoesNotResetManuallySetParent() {
+        put("source", "FALSE");
+        put("child", "ALARM(source) AND FALSE");
+        put("parent", "ALARM(child)");
+        service.setAlarmState("parent", "ALARM", "manual", null, REGION);
+        service.setAlarmState("source", "ALARM", "child condition remains false", null, REGION);
+        assertEquals("OK", state("child"));
+        assertEquals("ALARM", state("parent"));
+    }
+
+    @Test
+    void creationAndDeletionReevaluateOnlyReferencingComposites() {
+        MetricAlarm metric = new MetricAlarm();
+        metric.setAlarmName("late");
+        put("watcher", "INSUFFICIENT_DATA(late)");
+        put("outer", "ALARM(watcher)");
+        assertEquals("OK", state("watcher"));
+        service.putMetricAlarm(metric, REGION);
+        assertEquals("ALARM", state("watcher"));
+        assertEquals("ALARM", state("outer"));
+        service.deleteAlarms(List.of("late"), REGION);
+        assertEquals("OK", state("watcher"));
+        assertEquals("OK", state("outer"));
+    }
+
+    @Test
+    void tagReadIsAnIndependentSnapshotOfTheOwnedAlarm() {
+        CompositeAlarm alarm = put("tag-snapshot", "TRUE");
+        service.tagResource(alarm.getAlarmArn(), Map.of("team", "old"), REGION);
+        Map<String, String> read = service.listTagsForResource(alarm.getAlarmArn(), REGION);
+        service.tagResource(alarm.getAlarmArn(), Map.of("team", "new"), REGION);
+        assertEquals(Map.of("team", "old"), read);
+        read.put("injected", "unowned");
+        assertEquals(Map.of("team", "new"), service.listTagsForResource(alarm.getAlarmArn(), REGION));
+    }
+
+    @Test
+    void cyclesStopEvaluationEvenBehindShortCircuitAndMustBeBrokenBeforeDelete() {
+        put("a", "FALSE AND ALARM(b)");
+        put("b", "ALARM(a)");
+        service.setAlarmState("b", "ALARM", "manual", null, REGION);
+        assertThrows(AwsException.class, () -> service.deleteAlarms(List.of("a"), REGION));
+        assertEquals(2, service.describeCompositeAlarms(null, null, REGION).size());
+        put("a", "FALSE");
+        service.deleteAlarms(List.of("b"), REGION);
+        assertEquals("OK", state("a"));
+        service.deleteAlarms(List.of("a"), REGION);
+        assertTrue(service.describeCompositeAlarms(null, null, REGION).isEmpty());
+    }
+
+    @Test
+    void manuallyChangingOneMemberDoesNotResumeACyclicDependency() {
+        put("a", "ALARM(b)");
+        put("b", "ALARM(a)");
+        assertEquals("OK", state("a"));
+        service.setAlarmState("b", "ALARM", "manual", null, REGION);
+        assertEquals("OK", state("a"));
+        put("b", "TRUE");
+        service.setAlarmState("b", "ALARM", "cycle broken", null, REGION);
+        assertEquals("ALARM", state("a"));
+    }
+
+    @Test
+    void parentQuotaTreatsAChildNameAndItsArnAsTheSameAlarm() {
+        CompositeAlarm child = put("child", "FALSE");
+        for (int index = 0; index < 150; index++) {
+            put("parent-" + index, "ALARM(child)");
+        }
+        assertThrows(AwsException.class, () -> put("overflow", "ALARM(\"" + child.getAlarmArn() + "\")"));
+        service.deleteAlarms(List.of("parent-0"), REGION);
+        assertEquals("OK", put("replacement", "ALARM(\"" + child.getAlarmArn() + "\")").getStateValue());
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"", "ALARM()", "TRUE junk", "TRUE AND", "ALARM(\"unterminated)",
+            "(TRUE", "ALARM(x) XOR FALSE", "ALARM(\"x\\z\")"})
+    void invalidRulesDoNotReplaceAnExistingAlarm(String invalid) {
+        put("saved", "TRUE");
+        assertThrows(AwsException.class, () -> put("saved", invalid));
+        assertEquals("TRUE", service.describeCompositeAlarms(List.of("saved"), null, REGION).getFirst().getAlarmRule());
+        assertEquals("ALARM", state("saved"));
+    }
+
+    @Test
+    void quotasAndAtomicCreatePreventExcessReferencesAndForeignNameReplacement() {
+        String many = IntStream.range(0, 101).mapToObj(i -> "ALARM(a" + i + ")")
+                .collect(Collectors.joining(" OR "));
+        assertThrows(AwsException.class, () -> put("too-many", many));
+        put("owned", "TRUE");
+        CompositeAlarm foreign = new CompositeAlarm();
+        foreign.setAlarmName("owned");
+        foreign.setAlarmRule("FALSE");
+        assertThrows(AwsException.class, () -> service.putCompositeAlarm(foreign, REGION, false));
+        assertEquals("ALARM", state("owned"));
+        assertThrows(AwsException.class, () -> put("deep", "(".repeat(250) + "TRUE" + ")".repeat(250)));
+        assertEquals("ALARM", put("many-not", "NOT ".repeat(502) + "TRUE").getStateValue());
+        assertThrows(AwsException.class, () -> put("elements", "FALSE OR ".repeat(500) + "TRUE"));
+    }
+
+    @Test
+    void mixedPersistenceLoadsLegacyMetricsAndRoundTripsComposites() throws Exception {
+        ObjectMapper mapper = new ObjectMapper();
+        TypeReference<Map<String, Alarm>> type = new TypeReference<>() {};
+        Map<String, Alarm> legacy = mapper.readValue(
+                "{\"legacy\":{\"alarmName\":\"old\",\"metricName\":\"CPU\",\"stateValue\":\"OK\"}}", type);
+        assertInstanceOf(MetricAlarm.class, legacy.get("legacy"));
+        CompositeAlarm alarm = put("new", "FALSE");
+        Map<String, Alarm> restored = mapper.readValue(mapper.writeValueAsBytes(Map.of("new", alarm)), type);
+        assertEquals("FALSE", assertInstanceOf(CompositeAlarm.class, restored.get("new")).getAlarmRule());
+        assertEquals("OK", restored.get("new").getStateValue());
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void concurrentTagChangesPreserveTheUpdatedDefinition(boolean remove) throws Exception {
+        CountDownLatch updating = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        InMemoryStorage<String, Alarm> storage = new InMemoryStorage<>() {
+            @Override
+            public void put(String key, Alarm value) {
+                if (value instanceof CompositeAlarm composite && "TRUE".equals(composite.getAlarmRule())) {
+                    updating.countDown();
+                    try {
+                        assertTrue(release.await(5, TimeUnit.SECONDS));
+                    } catch (InterruptedException error) {
+                        Thread.currentThread().interrupt();
+                        throw new AssertionError(error);
+                    }
+                }
+                super.put(key, value);
+            }
+        };
+        CloudWatchMetricsService concurrent = new CloudWatchMetricsService(new InMemoryStorage<>(), storage,
+                new RegionResolver(REGION, "123456789012"));
+        CompositeAlarm original = new CompositeAlarm();
+        original.setAlarmName("concurrent");
+        original.setAlarmRule("FALSE");
+        original.setTags(new HashMap<>(Map.of("team", "old")));
+        concurrent.putCompositeAlarm(original, REGION);
+        CompositeAlarm replacement = new CompositeAlarm();
+        replacement.setAlarmName("concurrent");
+        replacement.setAlarmRule("TRUE");
+        AtomicReference<Thread> tagThread = new AtomicReference<>();
+        try (ExecutorService executor = Executors.newFixedThreadPool(2)) {
+            Future<?> update = executor.submit(() -> concurrent.putCompositeAlarm(replacement, REGION));
+            Future<?> tags;
+            try {
+                assertTrue(updating.await(2, TimeUnit.SECONDS));
+                tags = executor.submit(() -> {
+                    tagThread.set(Thread.currentThread());
+                    if (remove) {
+                        concurrent.untagResource(original.getAlarmArn(), List.of("team"), REGION);
+                    } else {
+                        concurrent.tagResource(original.getAlarmArn(), Map.of("team", "new"), REGION);
+                    }
+                });
+                ThreadStates.awaitBlockedOrDone(tagThread, tags);
+                assertFalse(tags.isDone(), "tag mutation must share the definition update lock");
+            } finally {
+                release.countDown();
+            }
+            update.get(2, TimeUnit.SECONDS);
+            tags.get(2, TimeUnit.SECONDS);
+        }
+        CompositeAlarm result = concurrent.describeCompositeAlarms(List.of("concurrent"), null, REGION).getFirst();
+        assertEquals("TRUE", result.getAlarmRule());
+        assertEquals(remove ? Map.of() : Map.of("team", "new"), result.getTags());
+    }
+
+    private CompositeAlarm put(String name, String rule) {
+        CompositeAlarm alarm = new CompositeAlarm();
+        alarm.setAlarmName(name);
+        alarm.setAlarmRule(rule);
+        alarm.setActionsEnabled(true);
+        service.putCompositeAlarm(alarm, REGION);
+        return alarm;
+    }
+
+    private String state(String name) {
+        return service.describeCompositeAlarms(List.of(name), null, REGION).getFirst().getStateValue();
+    }
+}
@@ -232,4 +232,29 @@ class CloudWatchMetricStreamsServiceTest {
        service.untagResource(arn, List.of("team"), REGION);
        assertFalse(service.listTagsForResource(arn, REGION).containsKey("team"));
    }
+
+    /**
+     * An ARN naming no stream is an error on all three operations, not a silent no-op. The ARN
+     * used here differs from a working one only in the stream name, so the outcome cannot be
+     * explained by the ARN failing to parse as a metric stream ARN.
+     */
+    @Test
+    void tagOperationsRejectAnArnThatNamesNoStream() {
+        String arn = service.putMetricStream(stream("ops"), REGION).getArn();
+        String ghost = arn.replace("metric-stream/ops", "metric-stream/nosuch");
+        assertTrue(CloudWatchMetricStreamsService.isMetricStreamArn(ghost));
+
+        for (Runnable call : List.<Runnable>of(
+                () -> service.tagResource(ghost, Map.of("env", "prod"), REGION),
+                () -> service.untagResource(ghost, List.of("env"), REGION),
+                () -> service.listTagsForResource(ghost, REGION))) {
+            AwsException e = assertThrows(AwsException.class, call::run);
+            assertEquals("ResourceNotFoundException", e.getErrorCode());
+            assertEquals(404, e.getHttpStatus());
+        }
+
+        // The failures wrote nothing: the real stream still carries only what it was given.
+        service.tagResource(arn, Map.of("team", "platform"), REGION);
+        assertEquals(Map.of("team", "platform"), service.listTagsForResource(arn, REGION));
+    }
 }
@@ -373,6 +373,63 @@ class CognitoServiceTest {
                null, null, List.of(), null, null);
    }

+    @Nested
+    class PreventUserExistenceErrors {
+
+        private UserPoolClient client(UserPool pool, String preventUserExistenceErrors) {
+            return service.createUserPoolClient(pool.getId(), "existence-client", false, false, List.of(), List.of(),
+                    null, List.of(), null, List.of("ALLOW_USER_PASSWORD_AUTH"), null, null, List.of(),
+                    preventUserExistenceErrors, List.of(), null, null, null, List.of(), null, null);
+        }
+
+        @Test
+        void enabledAnswersAnUnknownUserLikeAWrongPassword() {
+            UserPool pool = createPoolAndUser();
+            UserPoolClient client = client(pool, "ENABLED");
+
+            AwsException unknown = assertThrows(AwsException.class, () -> service.initiateAuth(client.getClientId(),
+                    "USER_PASSWORD_AUTH", Map.of("USERNAME", "nobody", "PASSWORD", "Perm1234!")));
+            AwsException wrongPassword = assertThrows(AwsException.class, () -> service.initiateAuth(client.getClientId(),
+                    "USER_PASSWORD_AUTH", Map.of("USERNAME", "alice", "PASSWORD", "Wrong1234!")));
+
+            assertEquals("NotAuthorizedException", unknown.getErrorCode());
+            assertEquals(wrongPassword.getErrorCode(), unknown.getErrorCode());
+            assertEquals(wrongPassword.getMessage(), unknown.getMessage());
+        }
+
+        @Test
+        void enabledSimulatesCodeDeliveryAndRejectsCodesForAnUnknownUser() {
+            UserPool pool = createPoolAndUser();
+            UserPoolClient client = client(pool, "ENABLED");
+
+            assertEquals(Map.of("AttributeName", "email", "DeliveryMedium", "EMAIL", "Destination", "n***@e***"),
+                    service.forgotPassword(client.getClientId(), "nobody@example.com"));
+            assertEquals("EMAIL", service.resendConfirmationCode(client.getClientId(), "nobody@example.com")
+                    .get("DeliveryMedium"));
+            assertEquals("CodeMismatchException", assertThrows(AwsException.class, () ->
+                    service.confirmForgotPassword(client.getClientId(), "nobody@example.com", "123456", "Perm1234!"))
+                    .getErrorCode());
+            assertEquals("CodeMismatchException", assertThrows(AwsException.class, () ->
+                    service.confirmSignUp(client.getClientId(), "nobody@example.com", "123456")).getErrorCode());
+            assertThrows(AwsException.class, () -> service.adminGetUser(pool.getId(), "nobody@example.com"),
+                    "no user is created along the way");
+        }
+
+        @Test
+        void legacyAndUnsetStillReportUserNotFound() {
+            UserPool pool = createPoolAndUser();
+            for (String setting : new String[] {"LEGACY", null}) {
+                UserPoolClient client = client(pool, setting);
+
+                assertEquals("UserNotFoundException", assertThrows(AwsException.class, () -> service.initiateAuth(
+                        client.getClientId(), "USER_PASSWORD_AUTH", Map.of("USERNAME", "nobody", "PASSWORD", "x")))
+                        .getErrorCode());
+                assertEquals("UserNotFoundException", assertThrows(AwsException.class, () ->
+                        service.forgotPassword(client.getClientId(), "nobody")).getErrorCode());
+            }
+        }
+    }
+
    @ParameterizedTest
    @CsvSource({
            "Short1!a",
@@ -1312,6 +1369,22 @@ class CognitoServiceTest {
        assertEquals("http://localhost:4566/custompool", service.getIssuer(pool.getId()));
    }

+    @Test
+    void localIssuerKeysServeOnlyThisEmulatorsOwnPoolIssuers() throws Exception {
+        UserPool pool = createPoolAndUser();
+        UserPoolClient client = clientWithFlows(pool, "ALLOW_USER_PASSWORD_AUTH");
+        String token = (String) ((Map<?, ?>) service.initiateAuth(client.getClientId(), "USER_PASSWORD_AUTH",
+                Map.of("USERNAME", "alice", "PASSWORD", "Perm1234!")).get("AuthenticationResult")).get("AccessToken");
+        String kid = MAPPER.readTree(Base64.getUrlDecoder().decode(token.split("\\.")[0])).path("kid").asText();
+
+        Map<String, java.security.interfaces.RSAPublicKey> keys = service.localIssuerKeys(service.getIssuer(pool.getId())).orElseThrow();
+        assertTrue(keys.containsKey(kid), "the key that signed the pool's tokens");
+        assertTrue(service.localIssuerKeys(service.getIssuer(pool.getId()) + "/").isPresent());
+        assertTrue(service.localIssuerKeys("https://cognito-idp.us-east-1.amazonaws.com/" + pool.getId()).isEmpty());
+        assertTrue(service.localIssuerKeys(service.getIssuer("us-east-1_missing")).isEmpty());
+        assertTrue(service.localIssuerKeys(null).isEmpty());
+    }
+
    // =========================================================================
    // Groups
    // =========================================================================
@@ -287,7 +287,8 @@ class SmtpRelayServerTest {
                String command = line.toUpperCase(Locale.ROOT);
                if (command.startsWith("EHLO")) {
                    reply(out, "250-floci-stub");
-                    reply(out, "250 AUTH PLAIN");
+                    // Gmail also offers OAuth sign-in, which a password must never be sent as.
+                    reply(out, "250 AUTH PLAIN XOAUTH2 OAUTHBEARER");
                } else if (command.startsWith("HELO")) {
                    reply(out, "250 floci-stub");
                } else if (command.startsWith("AUTH")) {
@@ -0,0 +1,199 @@
+package io.github.hectorvent.floci.testing;
+
+import io.restassured.path.xml.XmlPath;
+import io.restassured.path.xml.element.Node;
+import io.restassured.response.Response;
+import io.restassured.specification.RequestSpecification;
+
+import java.util.List;
+import java.util.Set;
+
+import static io.restassured.RestAssured.given;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.not;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/**
+ * DeleteStack answers before the stack is gone. The deletion runs on an executor, so a test
+ * that looks at the stack's resources right after the answer races it.
+ */
+public final class CfnStackWaits {
+
+    private CfnStackWaits() {
+    }
+
+    /** What DescribeStacks reported: the status and, when present, the StackStatusReason. */
+    public record StackState(String status, String reason) {
+    }
+
+    private static final Set<String> TERMINAL = Set.of(
+            "CREATE_COMPLETE", "CREATE_FAILED", "ROLLBACK_COMPLETE", "ROLLBACK_FAILED",
+            "UPDATE_COMPLETE", "UPDATE_FAILED", "UPDATE_ROLLBACK_COMPLETE", "UPDATE_ROLLBACK_FAILED",
+            "DELETE_COMPLETE", "DELETE_FAILED");
+
+    private static final Set<String> OPERATION_STARTS = Set.of("CREATE_IN_PROGRESS", "UPDATE_IN_PROGRESS");
+
+    /**
+     * Waits until DescribeStacks reports a terminal status for a create or update and returns
+     * it, so the caller decides what counts as success. A DescribeStacks that is not 200 (the
+     * stack does not exist) fails at once with the error body rather than polling the clock out;
+     * ten seconds without a terminal status fails too.
+     */
+    public static StackState awaitTerminal(String stackName) {
+        return awaitTerminal(stackName, null);
+    }
+
+    public static StackState awaitTerminal(String stackName, String authorization) {
+        long deadline = System.currentTimeMillis() + 10_000;
+        StackState last = new StackState(null, "");
+        while (System.currentTimeMillis() < deadline) {
+            RequestSpecification request = given()
+                .contentType("application/x-www-form-urlencoded")
+                .formParam("Action", "DescribeStacks")
+                .formParam("StackName", stackName);
+            if (authorization != null) {
+                request.header("Authorization", authorization);
+            }
+            Response response = request.when().post("/");
+            if (response.statusCode() != 200) {
+                fail("DescribeStacks " + stackName + " answered " + response.statusCode() + ": " + response.asString());
+            }
+            XmlPath xml = response.xmlPath();
+            String status = xml.getString("**.find { it.name() == 'StackStatus' }");
+            String reason = xml.getString("**.find { it.name() == 'StackStatusReason' }");
+            last = new StackState(status == null || status.isEmpty() ? null : status, reason == null ? "" : reason);
+            if (last.status() != null && TERMINAL.contains(last.status())) {
+                return last;
+            }
+            try {
+                Thread.sleep(50);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new AssertionError("Interrupted while waiting for stack " + stackName, e);
+            }
+        }
+        fail("Stack " + stackName + " reached no terminal status within ten seconds, last: " + last);
+        return last;
+    }
+
+    /**
+     * Waits until DescribeStacks reports {@code expectedStatus} and returns that state. Any other
+     * terminal status fails at once with its reason, as do a DescribeStacks that is not 200 and ten
+     * seconds without the expected status.
+     */
+    public static StackState awaitStatus(String stackName, String expectedStatus) {
+        long deadline = System.currentTimeMillis() + 10_000;
+        StackState last = new StackState(null, "");
+        while (System.currentTimeMillis() < deadline) {
+            Response response = given()
+                .contentType("application/x-www-form-urlencoded")
+                .formParam("Action", "DescribeStacks")
+                .formParam("StackName", stackName)
+                .when().post("/");
+            if (response.statusCode() != 200) {
+                fail("DescribeStacks " + stackName + " answered " + response.statusCode() + ": " + response.asString());
+            }
+            XmlPath xml = response.xmlPath();
+            String status = xml.getString("**.find { it.name() == 'StackStatus' }");
+            String reason = xml.getString("**.find { it.name() == 'StackStatusReason' }");
+            last = new StackState(status == null || status.isEmpty() ? null : status, reason == null ? "" : reason);
+            if (expectedStatus.equals(last.status())) {
+                return last;
+            }
+            if (last.status() != null && TERMINAL.contains(last.status())) {
+                fail("Stack " + stackName + " reached " + last.status() + " instead of " + expectedStatus
+                        + ": " + last.reason());
+            }
+            try {
+                Thread.sleep(50);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new AssertionError("Interrupted while waiting for stack " + stackName, e);
+            }
+        }
+        fail("Stack " + stackName + " did not reach " + expectedStatus + " within ten seconds, last: " + last);
+        return last;
+    }
+
+    /**
+     * The reason on the first resource event that failed a create or update in the stack's latest
+     * operation, the one its last stack-level CREATE_IN_PROGRESS or UPDATE_IN_PROGRESS began. The
+     * stack's own reason only names the failed resource, as on AWS, so the failure's message is read
+     * here. Fails when DescribeStackEvents is not 200 or no resource failed in that operation.
+     */
+    public static String failedResourceReason(String stackName) {
+        return failedResourceReason(stackName, null);
+    }
+
+    public static String failedResourceReason(String stackName, String authorization) {
+        RequestSpecification request = given()
+            .contentType("application/x-www-form-urlencoded")
+            .formParam("Action", "DescribeStackEvents")
+            .formParam("StackName", stackName);
+        if (authorization != null) {
+            request.header("Authorization", authorization);
+        }
+        Response response = request.when().post("/");
+        if (response.statusCode() != 200) {
+            fail("DescribeStackEvents " + stackName + " answered " + response.statusCode() + ": " + response.asString());
+        }
+        List<Node> newestFirst = response.xmlPath().getList("**.findAll { it.name() == 'member' }", Node.class);
+        String reason = null;
+        for (Node event : newestFirst) {
+            String status = text(event, "ResourceStatus");
+            if (text(event, "StackName").equals(text(event, "LogicalResourceId"))
+                    && text(event, "StackId").equals(text(event, "PhysicalResourceId"))) {
+                if (OPERATION_STARTS.contains(status)) {
+                    break;
+                }
+            } else if ("CREATE_FAILED".equals(status) || "UPDATE_FAILED".equals(status)) {
+                reason = text(event, "ResourceStatusReason");
+            }
+        }
+        if (reason == null) {
+            fail("Stack " + stackName + " has no failed resource event in its latest operation: " + response.asString());
+        }
+        return reason;
+    }
+
+    private static String text(Node event, String name) {
+        Node child = event.getNode(name);
+        return child == null ? "" : child.value();
+    }
+
+    /**
+     * Waits until DescribeStacks answers 400, which is how a missing stack is reported. Fails on
+     * DELETE_FAILED or after ten seconds.
+     */
+    public static void awaitStackDeleted(String stackName) {
+        awaitStackDeleted(stackName, null);
+    }
+
+    public static void awaitStackDeleted(String stackName, String authorization) {
+        long deadline = System.currentTimeMillis() + 10_000;
+        String body = "";
+        while (System.currentTimeMillis() < deadline) {
+            RequestSpecification request = given()
+                .contentType("application/x-www-form-urlencoded")
+                .formParam("Action", "DescribeStacks")
+                .formParam("StackName", stackName);
+            if (authorization != null) {
+                request.header("Authorization", authorization);
+            }
+            Response response = request.when().post("/");
+            body = response.asString();
+            assertThat(body, not(containsString("<StackStatus>DELETE_FAILED</StackStatus>")));
+            if (response.statusCode() == 400) {
+                return;
+            }
+            try {
+                Thread.sleep(50);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new AssertionError("Interrupted while waiting for stack " + stackName + " to be deleted", e);
+            }
+        }
+        fail("Stack " + stackName + " was not deleted within ten seconds: " + body);
+    }
+}
@@ -0,0 +1,47 @@
+package io.github.hectorvent.floci.testing;
+
+import org.junit.jupiter.api.extension.AfterEachCallback;
+import org.junit.jupiter.api.extension.ExtensionContext;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * Deletes what a test created, in reverse order, after each test. The {@code @QuarkusTest}
+ * emulator is shared by every test class, so a resource left behind outlives the class that made
+ * it: one under {@code cn-north-1} shows up in every later cross-region listing (ResourceExplorer
+ * scans all resources), and an IAM user or an S3 bucket shows up in the next class to list either
+ * one unscoped. A test that leaves such a resource registers each create here.
+ *
+ * <pre>{@code
+ * @RegisterExtension
+ * final PartitionCleanup cleanup = new PartitionCleanup();
+ * ...
+ * createTable(region, name);
+ * cleanup.register(() -> deleteTable(region, name));
+ * }</pre>
+ *
+ * A failing cleanup never fails the test: it is reported on stderr so the leak is visible and
+ * the assertion that actually failed stays the headline.
+ */
+public final class PartitionCleanup implements AfterEachCallback {
+
+    private final Deque<Runnable> actions = new ArrayDeque<>();
+
+    public void register(Runnable action) {
+        actions.push(action);
+    }
+
+    @Override
+    public void afterEach(ExtensionContext context) {
+        while (!actions.isEmpty()) {
+            Runnable action = actions.pop();
+            try {
+                action.run();
+            } catch (RuntimeException | AssertionError e) {
+                System.err.println("PartitionCleanup: cleanup step failed after "
+                        + context.getDisplayName() + ": " + e);
+            }
+        }
+    }
+}
@@ -0,0 +1,93 @@
+package io.github.hectorvent.floci.testing;
+
+import java.time.Duration;
+import java.util.Collections;
+import java.util.EnumSet;
+import java.util.Set;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.LockSupport;
+import java.util.function.BooleanSupplier;
+import java.util.function.Supplier;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/** Waiting for a thread to reach a lock, for tests that force two requests to overlap. */
+public final class ThreadStates {
+
+    /** Every state a thread is in once it has stopped running: parked in any way, or ended. */
+    public static final Set<Thread.State> PARKED_OR_DONE = Collections.unmodifiableSet(EnumSet.of(
+            Thread.State.BLOCKED, Thread.State.WAITING, Thread.State.TIMED_WAITING, Thread.State.TERMINATED));
+
+    private ThreadStates() {}
+
+    /**
+     * Returns once {@code thread} is blocked entering a monitor or parked on a lock, or {@code task} has
+     * finished, whichever comes first. Code that serializes correctly leaves the second request blocked
+     * behind the first; code that does not lets it run to the end, which the caller's assertions
+     * then catch. Polls every 5 ms and gives up after five seconds rather than hang a broken test.
+     */
+    public static void awaitBlockedOrDone(AtomicReference<Thread> thread, Future<?> task)
+            throws InterruptedException {
+        awaitBlockedOrDone(thread::get, task::isDone, 5);
+    }
+
+    /**
+     * Returns once {@code thread} is blocked entering a monitor, parked on a lock, or is no longer alive.
+     * Same wait as the {@link Future} overload, for a test that owns the {@link Thread} directly; gives up
+     * after ten seconds and fails, since a thread still running unblocked by then is not overlapping the
+     * way the test needs.
+     */
+    public static void awaitBlockedOrDone(Thread thread) throws InterruptedException {
+        assertTrue(awaitBlockedOrDone(() -> thread, () -> !thread.isAlive(), 10),
+                "worker blocked or finished before timeout");
+    }
+
+    private static boolean awaitBlockedOrDone(Supplier<Thread> thread, BooleanSupplier done, long timeoutSeconds)
+            throws InterruptedException {
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds);
+        while (System.nanoTime() < deadline && !done.getAsBoolean()) {
+            if (isBlocked(thread.get())) {
+                return true;
+            }
+            Thread.sleep(5);
+        }
+        return done.getAsBoolean() || isBlocked(thread.get());
+    }
+
+    private static boolean isBlocked(Thread thread) {
+        if (thread == null) {
+            return false;
+        }
+        Thread.State state = thread.getState();
+        return state == Thread.State.BLOCKED || state == Thread.State.WAITING;
+    }
+
+    /**
+     * Waits until {@code thread} is parked in any way (blocked on a monitor, waiting or timed
+     * waiting) or has ended, and returns the state it reached. Fails after ten seconds.
+     */
+    public static Thread.State awaitParkedOrDone(Thread thread) {
+        return awaitState(thread, PARKED_OR_DONE, Duration.ofSeconds(10), "the thread");
+    }
+
+    /**
+     * Waits until {@code thread} is in one of {@code states} and returns the one it reached, checking
+     * every millisecond. Fails naming {@code what} and the state it was left in once {@code timeout}
+     * passes, so a thread that never gets there fails the test instead of hanging it.
+     */
+    public static Thread.State awaitState(Thread thread, Set<Thread.State> states, Duration timeout, String what) {
+        long deadline = System.nanoTime() + timeout.toNanos();
+        Thread.State state = thread.getState();
+        while (!states.contains(state)) {
+            if (System.nanoTime() - deadline > 0) {
+                fail(what + " never reached " + states + ", it was " + state);
+            }
+            LockSupport.parkNanos(TimeUnit.MILLISECONDS.toNanos(1));
+            state = thread.getState();
+        }
+        return state;
+    }
+}
@@ -41,6 +41,7 @@ AWS::CloudFront::OriginRequestPolicy	CloudFrontCfnProvisioner
 AWS::CloudFront::ResponseHeadersPolicy	CloudFrontCfnProvisioner
 AWS::CloudTrail::Trail	CloudTrailCfnProvisioner
 AWS::CloudWatch::Alarm	CloudWatchCfnProvisioner
+AWS::CloudWatch::CompositeAlarm	CloudWatchCompositeAlarmCfnProvisioner
 AWS::CloudWatch::Dashboard	CloudWatchDashboardCfnProvisioner
 AWS::CodeBuild::Project	CodeBuildCfnProvisioner
 AWS::CodePipeline::CustomActionType	CodePipelineCfnProvisioner
@@ -169,6 +169,9 @@ notes:
 # Trailing prose appended to a row after its type list, for behaviour that belongs to the service
 # rather than to one type.
 row_notes:
+  AWS::CloudWatch: >-
+    Composite alarms have backing definitions with name Ref and Arn GetAtt, rollback, and
+    replacement cleanup. Composite actions are stored only; suppression properties are rejected.
  AWS::Lambda: >-
    Inline `ZipFile` packages include the `cfn-response` (Node.js) / `cfnresponse` (Python) module
    AWS injects for that code path, so Solutions-style custom-resource handlers work.
Author	SHA1	Message	Date
Zakaria	eaf5ca6ade	Merge pull request 'docs: rebrand the README as TheCloud's AWS runtime' (#11 ) from docs/readme-thecloud into main Reviewed-on: #11	2026-10-25 14:29:43 +00:00
Zakaria	cc64729599	docs: rebrand the README as TheCloud's AWS runtime Use TheCloud's logo and name, describe the repository as the fork of Floci behind TheCloud with its own changes, and replace instructions for upstream's published artifacts (Floci CLI, Docker Hub tags and release train) with building and running this repository. Drop the upstream badges, comparison table, community, sponsor, star-history and contributor sections, keep literal identifiers (FLOCI_* settings, upstream package names), and credit Floci under License.	2026-10-25 10:11:34 -04:00
Zakaria	9f17f72cc3	Merge pull request 'fix(apigatewayv2): verify tokens from Floci's own Cognito pools in-process' (#10 ) from fix/apigatewayv2-local-cognito-issuer into main Reviewed-on: #10	2026-10-25 13:49:41 +00:00
Zakaria	d8d94a773d	fix(apigatewayv2): verify tokens from Floci's own Cognito pools in-process A JWT authorizer on one of Floci's own user pools could never pass: the pool's issuer is Floci's base URL (plain HTTP on localhost or a Compose service name), and the verifier only fetches discovery and JWKS documents over HTTPS or from a private IP literal. When the configured issuer is exactly one of this emulator's pool issuers, read the pool's signing keys directly; they are the keys it publishes at its JWKS URL. Every other issuer keeps the strict fetch.	2026-10-25 08:57:05 -04:00
Zakaria	957579c8b7	Merge pull request 'fix(cognito): honour PreventUserExistenceErrors=ENABLED on app clients' (#9 ) from fix/cognito-prevent-user-existence-errors into main Reviewed-on: #9	2026-10-25 12:27:48 +00:00
Zakaria	d9a1a36dc8	fix(cognito): honour PreventUserExistenceErrors=ENABLED on app clients The setting was stored but never applied, so an unknown username always got UserNotFoundException and revealed which accounts exist. With ENABLED, answer as real Cognito does: password sign-in fails with NotAuthorizedException "Incorrect username or password", ForgotPassword and ResendConfirmationCode report a simulated delivery, and ConfirmForgotPassword and ConfirmSignUp fail with CodeMismatchException. LEGACY and unset keep UserNotFoundException. SRP and USER_AUTH flows are unchanged.	2026-10-25 08:26:34 -04:00
Zakaria	5d4b010710	Merge pull request 'fix(ses): sign in to the SMTP relay with the password, not as an OAuth token' (#8 ) from fix/ses-smtp-password-auth into main Reviewed-on: #8	2026-10-25 11:57:20 +00:00
Zakaria	2486869b6b	fix(ses): sign in to the SMTP relay with the password, not as an OAuth token Vert.x mail prefers XOAUTH2 whenever the server offers it, so against Gmail the app password was sent as an OAuth token and refused (535 5.7.8). Limit the relay to the password-based SASL methods.	2026-10-25 07:52:52 -04:00
Zakaria	327173c8f6	Merge pull request 'chore(docker): read optional SES SMTP relay settings from ~/.config/thecloud/ses-smtp.env' (#7 ) from feat/ses-smtp-relay-env into main Reviewed-on: #7	2026-10-25 11:46:41 +00:00
Zakaria	dcb007f8b8	chore(docker): read optional SES SMTP relay settings from ~/.config/thecloud/ses-smtp.env	2026-10-25 07:44:42 -04:00
Zakaria	607ac0803b	Merge pull request 'fix(cloudwatch): retain metric-math alarm query definitions (#4594 )' (#6 ) from feat/cloudwatch-upstream-fixes into main Reviewed-on: #6	2026-10-25 03:08:55 +00:00
Zakaria	a9df81a294	chore: add the upstream helpers the composite alarm change builds on Composite alarms from upstream (#6408) use SmithyValidationErrors for AWS's validation messages, and their tests use the CfnStackWaits, PartitionCleanup and ThreadStates test helpers and ReplacementCleanup.owedPhysicalIds. These are copied from upstream as they were at that commit; none brings in other behaviour.	2026-10-24 22:23:29 -04:00
Andre Kurait	fa3327bf71	feat(cloudwatch): support composite alarm lifecycle (#6408 ) (cherry picked from commit 922e36a472341861e97d1b5639656f3c4a3978d8)	2026-10-24 22:23:29 -04:00
Stuart Lang	83aafc0325	fix(cloudwatch): return empty CompositeAlarms and LogAlarms from DescribeAlarms (#6363 ) * fix(cloudwatch): return empty CompositeAlarms and LogAlarms from DescribeAlarms AWS sends every alarm collection even when it is empty. Floci only sent MetricAlarms, so the AWS CLI's text output printed a leading None line for each missing paginator result key. Closes #6362 * test(cloudwatch): check empty alarm collections in sdk-test-python instead of bats Drop the new AWS CLI bats file and assert the empty CompositeAlarms and LogAlarms lists in the existing describe_alarms test, as boto3 leaves an absent list out of the response. (cherry picked from commit 42f5019231b446c727d6c94def9d1445263de2d7)	2026-10-24 22:19:09 -04:00
Mohith	24314f4432	fix(cloudwatch): reject PutMetricData datums without a MetricName (#6072 ) * fix(cloudwatch): reject PutMetricData datums without a MetricName MetricName is the one required member of MetricDatum. The JSON handler stored a nameless datum under an empty name, and the Query handler treated a member without MetricName as the end of the list, silently dropping it and every later datum while still storing the earlier ones. Both handlers now reject a missing or empty MetricName in top-level MetricData and in EntityMetricData[].MetricData with MissingParameter (400), the error PutMetricData declares for a missing required input, naming the offending member. A whitespace name is still accepted, since AWS constrains MetricName only to 1 to 255 characters. Every datum is validated before any is stored, so a rejected request leaves no state behind. On Query, a member index with no keys at all still ends that MetricData list. * fix(cloudwatch): return MissingRequiredParameterException on JSON and CBOR CloudWatch is awsQueryCompatible. MissingParameter is the awsQueryError code of the MissingRequiredParameterException shape, so it belongs in the Query <Code> and the x-amzn-query-error header, while a JSON 1.0 or CBOR body's __type names the shape. With the code in __type the AWS SDK v2 raised a generic CloudWatchException instead of the modelled one. A package-private CloudWatchMetricsException keeps the Query code as its error code and overrides jsonType() with the shape name, the same split SwfException makes. The shared query-code table in AwsException is left alone because SQS reports MissingParameter as its JSON type. (cherry picked from commit b8d87df05413ea8c4f9497fa05f388c19d4124ec)	2026-10-24 22:19:09 -04:00
Zakaria	e90978ae94	fix(cloudwatch): name the alarm's region without the partition catalog The SNS alarm notification from upstream (#5918) looks up the region's display name in AwsPartitions, which upstream added in a partition rework not taken here. A table of the commercial regions' names gives the same Region field.	2026-10-24 22:19:09 -04:00
Mohith	21625c5a1b	fix(cloudwatch): store datums sent in PutMetricData EntityMetricData (#6070 ) The CloudWatch Agent sends PutMetricData with an empty top-level MetricData and every datum nested under EntityMetricData[].MetricData. Both the JSON 1.0 handler (also reached by Smithy RPC v2 CBOR) and the Query handler read only the top-level list, so the agent's metrics were silently dropped. Both handlers now append each EntityMetricData entry's datums to the top-level ones and store them under the request Namespace, with the same parsing as top-level datums. Entity and StrictEntityValidation are accepted and ignored. The per-request INFO logs of the raw request and parsed datums are lowered to a DEBUG count. Fixes #6066 (cherry picked from commit 03f57303969561b049c3ebba38f1fd9d2b68df4c)	2026-10-24 22:19:09 -04:00
mrjusepelo	2e0a438d70	fix(cloudwatch): publish SNS actions on alarm state transitions (#5918 ) (cherry picked from commit f5811c3a0735be634b6122503237330826e0ba4a)	2026-10-24 22:17:17 -04:00
Allen Sanborn	ccdf32335d	fix(cloudwatch): raise ResourceNotFoundException when a tag operation names a resource that does not exist (#4783 ) * fix(cloudwatch): raise ResourceNotFoundException when a tag operation names a resource that does not exist TagResource, UntagResource and ListTagsForResource answered 200 for any ARN, so tagging a typo'd or deleted alarm, dashboard or metric stream told the caller the tag had been applied. AWS raises ResourceNotFoundException. All three operations now resolve the ARN first and report a 404 when nothing answers to it. The fix sits in the three services rather than in the handlers, because CloudWatch Metrics serves these operations over both Query and JSON 1.1 and the two handlers route to the same service methods. A handler-level check would have left the other protocol still answering 200. What the 200 was hiding is worth naming, because "return an error instead of 200" understates it. The write path resolved the ARN and then did nothing with the miss: tagResource and untagResource each ended in an ifPresent, so a tag against an unknown ARN was discarded, and ListTagsForResource answered the empty map. So the ARN was neither rejected nor recorded. Nothing was stored against a phantom resource, which is the one mercy here, but a caller that wrote a tag and read back an empty list had no way to tell "this resource has no tags" from "this resource does not exist". That is why ListTagsForResource is included rather than left alone. It is the one operation whose answer changes for a caller doing a speculative list, and the one whose leniency made the silent write survive a round trip. No test or caller in the repository depended on the empty-map answer for an unknown ARN: the only internal caller is CloudWatchDashboardCfnProvisioner.reconcileTags, and both of its call sites pass an ARN that putDashboard has just returned. The error code is ResourceNotFoundException, not the shorter ResourceNotFound that GetDashboard, DeleteDashboards and SetAlarmState answer with. Those are two separate shapes in the CloudWatch model, mapped to two exception classes by the SDK, and the model declares the longer one on exactly these three operations. CloudWatch Logs needed no change. Its own TagResource, UntagResource and ListTagsForResource already resolve the log group and raise ResourceNotFoundException, which the new test pins so the two halves of CloudWatch tagging cannot diverge in the other direction. * fix(cloudwatch): resolve a dashboard by either the regionless or the region-ful form of its ARN Dashboards are a global resource and AWS documents their ARN without a region, arn:aws:cloudwatch::<account-id>:dashboard/<dashboard-name>, on both the TagResource and the ListTagsForResource pages. Floci mints a region-ful one. The dashboard lookup now accepts both shapes deliberately, so a caller holding either resolves. Accepting both is what stops the preceding commit regressing a caller that does the documented thing. Until the tag operations raised on a miss, the divergence was invisible on this path: the documented ARN matched no stored dashboard, and the answer was a silent 200 with an empty tag map. Turning a miss into ResourceNotFoundException would have turned that into a hard 404 for a dashboard that exists. Only an absent region stands in for the dashboard's own, so an ARN naming some other region is still a miss and does not resolve to a same-named dashboard here. What Floci mints is not changed. Clients may already hold the ARNs it has handed out, so bringing the minted shape into line with AWS alters values already in circulation and belongs in its own change; it is tracked separately. The tolerant lookup is all that is needed to keep this path correct, and it is strictly more permissive than before, so it cannot break a caller that works today. Alarms and metric streams were checked rather than assumed: both mint region-ful ARNs and AWS documents both region-ful, so the question is dashboards only. Also reworded the not-found message on the alarm path to name the ARN that did not resolve instead of asserting it was an alarm. Both tag handlers route every ARN that is not a dashboard and not a metric stream to that path, including kinds AWS considers taggable and Floci does not serve, a Contributor Insights insight-rule ARN being the one AWS documents. Reporting that no resource matches the ARN is true of those; "alarm not found" was not. No Contributor Insights support is added here. * test(cloudwatch): assert a refused tag call left the real resource untagged The not-found tests tagged the unknown ARN env=prod and then re-tagged the real resource env=dev before reading it back, so a failed call that had written through to the real resource would have been overwritten and the assertion would still pass. Read the real resource's tags first; they must be empty. * test(cloudwatch): import matchers and use configureAwsContentTypes Import Matchers.not and java.util.Map in the new tests instead of writing them inline, register the x-amz-json content types through RestAssuredJsonUtils.configureAwsContentTypes() in place of registerParser and the hand-built encoder config, and drop DeleteDashboards from the requireDashboard Javadoc: only GetDashboard declares ResourceNotFound. (cherry picked from commit 0c8d1848541392ff91991121d96586db564cb3f8)	2026-10-24 22:17:17 -04:00
Aniket Shukla	cbb95ba26c	fix(cloudwatch): retain metric-math alarm query definitions (#4594 ) * fix(cloudwatch): retain metric-math alarm query definitions * test(cloudwatch): use shared XML parser for alarm assertions (cherry picked from commit 1d646c6fea70a8d4bfeea4d0ca6d8fc390ea6170)	2026-10-24 22:17:17 -04:00
Zakaria	90d5dc9427	Merge pull request 'fix(cognito): keep revoked tokens across restarts' (#5 ) from fix/cognito-revoked-tokens-reload into main Reviewed-on: #5	2026-10-24 18:52:58 +00:00