Cloudwatch alarm for 5xx API responses doesn't work

[asjohnston-asf]

Our API alarm specifies ApiId, but the cloudwatch docs suggest the correct dimension is ApiName. The metric is 5xx, but should be 5XXError.

https://github.com/ASFHyP3/hyp3/blob/develop/apps/monitoring-cf.yml.j2#L34

https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-metrics-and-dimensions.html

The alarm is created, but the metric always reports as No Data even when there are 5xx responses, so the alarm never triggers and no SNS message is ever sent.

[asjohnston-asf]

This issue was introduced in v2.11.0 when the API Gateway was converted from a HTTP API to a REST API. The CloudWatch metric and dimension names differ between the two types of APIs:

• REST APIs: https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-metrics-and-dimensions.html
• HTTP APIs: https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-metrics.html

[asjohnston-asf]

Unfortunately, there is no straightforward way to retrieve the auto-generated API name for use by the CloudWatch Alarm. I've opened https://github.com/aws-cloudformation/cloudformation-coverage-roadmap/issues/1918 requesting that feature.