private void processCloudWatchAlarmMessage()

in cloudwatch-lambda/src/main/java/com/amazonwebservices/blogs/containers/CloudWatchAlarmHandler.java [115:200]
65 lines of code
8 McCabe index (conditional complexity)

	private void processCloudWatchAlarmMessage (JsonObject alarmMessageObject) {
		logger.info(alarmMessageObject);
		
		String alarmName = alarmMessageObject.getString("AlarmName");
		String accountID = alarmMessageObject.getString("AWSAccountId");
		String alarmTriggerReason = alarmMessageObject.getString("NewStateReason");
		String alarmArn = String.format("arn:aws:cloudwatch:%s:%s:alarm:%s", AWS_REGION, accountID, alarmName);
		ComparisonOperator operator = Enum.valueOf(ComparisonOperator.class, alarmMessageObject.getJsonObject("Trigger").getString("ComparisonOperator"));
		
		logger.info(String.format("Alarm ARN = %s", alarmArn));
		logger.info(String.format("Reason for Trigger = %s", alarmTriggerReason));
		
		//
		// Get the name/namespace of the K8sMetricAlarm custom resource from the tags associated with the CloudWatch alarm
		//
		ListTagsForResourceRequest request = new ListTagsForResourceRequest().withResourceARN(alarmArn);
		ListTagsForResourceResult response = cloudWatchClient.listTagsForResource(request);
		List<Tag> tags = response.getTags();
		String resourceName = null;
		String resoueceNamespace = null;
		for (Tag t : tags) {
			switch (t.getKey()) {
				case K8S_NAME:
					resourceName = t.getValue();
					break;
				case K8S_NAMESPACE:
					resoueceNamespace = t.getValue();
					break;
				default:
					break;
			}
		}
		if (resourceName == null || resoueceNamespace == null) {
			logger.error(String.format("Unable to identify the Kubernetes name and namespace of the K8sMetricAlarm custom resource for alarm '%s'", alarmName));
			return;
		}
		
		//
		// Fetch the K8sMetricAlarm custom resource from the API server
		// The custom resource contains the name of the Deployment resource to be scaled
		//
		logger.info(String.format("Retrieving K8sMetricAlarm custom resource '%s.%s'", resourceName, resoueceNamespace));
		K8sMetricAlarmCustomObject cloudWatchAlarm = apiCloudWatchAlarm.get(resoueceNamespace, resourceName).getObject();
		String alarmStateResetReason;
		if (cloudWatchAlarm != null) {
			K8sMetricAlarmCustomObjectSpec cloudWatchAlarmSpec = cloudWatchAlarm.getSpec();
			int minReplicas = cloudWatchAlarmSpec.getMinReplicas();
			int maxReplicas = cloudWatchAlarmSpec.getMaxReplicas();
			ScalingBehavior scaleUpBehavior = cloudWatchAlarmSpec.getScaleUpBehavior();
			ScalingBehavior scaleDownBehavior = cloudWatchAlarmSpec.getScaleDownBehavior();
			String deploymentName = cloudWatchAlarmSpec.getDeployment();

			//
			// Fetch the Deployment resource from the API server
			// Compute the number of replicas to be scaled up or down based on scaling policies
			// Update the Deployment resource with the new number of replicas.
			//
			logger.info(String.format("Retrieving Deployment resource '%s.%s'", deploymentName, resoueceNamespace));
			V1Deployment deployment = apiDeployment.get(resoueceNamespace, deploymentName).getObject();
			V1ObjectMeta metadata = deployment.getMetadata();
			boolean isCoolingDown = isResourceCoolingDown (metadata, operator, scaleUpBehavior, scaleDownBehavior);
			if (isCoolingDown) {
				alarmStateResetReason = String.format("Deployment '%s.%s' is still cooling down. Suspending further scaling", deploymentName, resoueceNamespace);
				logger.info(alarmStateResetReason);
			}
			else {
				int replicas = deployment.getSpec().getReplicas();
				int scaledReplicas = computeScaling(operator, minReplicas, maxReplicas, replicas, scaleUpBehavior, scaleDownBehavior);
				updateDeployment(deployment, metadata, replicas, scaledReplicas, alarmName, alarmTriggerReason);
				alarmStateResetReason = String.format("Scaled Deployment '%s.%s' from %d to %d replicas", resoueceNamespace, deploymentName, replicas, scaledReplicas);
			}
		} else {
			alarmStateResetReason = String.format("Unable to retrieve K8sMetricAlarm custom resource '%s.%s'", resoueceNamespace, resourceName);
			logger.error(alarmStateResetReason);
		}
		
		//
		// After the scaling activity is completed/suspended, set the alarm status to OK
		//
		SetAlarmStateRequest setStateRequest = new SetAlarmStateRequest()
				.withAlarmName(alarmName)
				.withStateReason(alarmStateResetReason)
				.withStateValue(StateValue.OK);
		cloudWatchClient.setAlarmState(setStateRequest);
		logger.info(String.format("State of alarm '%s' set to %s", alarmName, StateValue.OK.toString()));
	}