compatibility-tests/sdk-test-python/tests/test_cloudwatch.py

@@ -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])
 

src/main/java/io/github/hectorvent/floci/services/cloudwatch/metrics/CloudWatchMetricsJsonHandler.java

@@ -263,6 +263,8 @@ public class CloudWatchMetricsJsonHandler {
             if (a.getStateReasonData() != null) node.put("StateReasonData", a.getStateReasonData());
             node.put("StateUpdatedTimestamp", a.getStateUpdatedTimestamp());
         }
+        response.putArray("CompositeAlarms");
+        response.putArray("LogAlarms");
         return Response.ok(response).build();
     }
 

src/main/java/io/github/hectorvent/floci/services/cloudwatch/metrics/CloudWatchMetricsQueryHandler.java

@@ -259,6 +259,8 @@ public class CloudWatchMetricsQueryHandler {
             toAlarmXml(xml, a);
         }
         xml.end("MetricAlarms");
+        xml.start("CompositeAlarms").end("CompositeAlarms");
+        xml.start("LogAlarms").end("LogAlarms");
         return Response.ok(AwsQueryResponse.envelope("DescribeAlarms", null, xml.build())).build();
     }
 

src/test/java/io/github/hectorvent/floci/services/cloudwatch/metrics/CloudWatchMetricsJsonHandlerTest.java

@@ -350,6 +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.

src/test/java/io/github/hectorvent/floci/services/cloudwatch/metrics/CloudWatchMetricsQueryHandlerTest.java

@@ -242,4 +242,15 @@ class CloudWatchMetricsQueryHandlerTest {
         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);
+    }
 }