How to create an EventBridge (CloudWatch Events) rule and add it to a Lambda function as a trigger using CDK?

Question

I'm trying to create an EventBridge (CloudWatch Events) Rule and have that rule added as a trigger to an existing Lambda function.

    const notificationFunction = lambda.Function.fromFunctionArn(this,
      'DevopsNotificationLambda',
      _props.notificationLambdaArn
    );
    const rule = new Rule(this, `${stackPrefix}-EventRule`, {
      eventPattern: {
        source: ['aws.codepipeline'],
        detailType: ['CodePipeline Pipeline Execution State Change'],
        detail: {pipeline: [pipeline.pipelineName]}
      },
    });
    notificationFunction.addPermission(`${stackPrefix}-CloudWatchPermission`, {
      principal: new ServicePrincipal('events.amazonaws.com'),
      sourceArn: rule.ruleArn
    });
    rule.addTarget(new LambdaFunction(notificationFunction));

The code creates the EventBridge with the Lambda target correctly, but it doesn't add the trigger to the actual Lambda. I have to manually add the EventBridge to the Lambda through the AWS Web Console.

Seems like it's not enough to add the Lambda as a target to the Event Rule. How should I add the Event Rule as a trigger to the Lambda?

Answer 1

From Importing existing external resources in the CDK Developer Guide.

Although you can use an imported resource anywhere, you cannot modify the imported resource. For example, calling addToResourcePolicy (Python: add_to_resource_policy) on an imported s3.Bucket does nothing.

You cannot add a trigger to notificationFunction from the CDK stack because notificationFunction is an external resource.