‼️ (aws-cloudwatch): cross account alarms cause failures in unsupported regions

[eladb]

Workaround is available 👇

What is the problem?

When deploying an @aws-cdk/aws-cloudwatch.Alarm in regions with no support for cross-account alarms, the deployment fails with the following error:

Encountered unsupported property AccountId

This is because the change in #16007 always adds an AccountId to metrics.

Reproduction Steps

Define a CDK stack with an AWS CloudWatch Alarm and deploy it to a region that still does not have support for cross-account alarms.

What did you expect to happen?

Success

What actually happened?

Encountered unsupported property AccountId

CDK CLI Version

1.126.0

Framework Version

1.126.0

Node.js Version

N/A

OS

N/A

Language

Typescript, Python, .NET, Java, Go

Language Version

N/A

Other information

Ref: P53531109

Workaround

You can delete the AccountId property by locating the CfnResource behind the cloudwatch.Alarm construct and then calling addPropertyDeletionOverride.

Consider the following example:

const alarm = new cloudwatch.Alarm(this, 'Alarm', {
  threshold: 1,
  evaluationPeriods: 1,
  metric: new cloudwatch.Metric({
    label: 'MyMetric',
    account: this.account,
    namespace: 'AWS/DynamoDB',
    metricName: 'ReadThrottleEvents',
    dimensionsMap: {
      TableName: 'MyTable'
    },
    statistic: 'Sum'
  }),
});

This is how the AWS::CloudWatch::Alarm is synthesized:

Alarm7103F465:
    Type: AWS::CloudWatch::Alarm
    Properties:
      ComparisonOperator: GreaterThanOrEqualToThreshold
      EvaluationPeriods: 1
      Metrics:
        - AccountId: "123456789012"
          Id: m1
          Label: MyMetric
          MetricStat:
            Metric:
              Dimensions:
                - Name: TableName
                  Value: MyTable
              MetricName: ReadThrottleEvents
              Namespace: AWS/DynamoDB
            Period: 300
            Stat: Sum
          ReturnData: true
      Threshold: 1

The following code will delete the AccountId property from the metric at index 0 (Metrics.0) in the alarm:

const cfnAlarm = alarm.node.defaultChild as CfnResource;
cfnAlarm?.addPropertyDeletionOverride('Metrics.0.AccountId');

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