Unable to create two CloudWatch Rules with the same target

[0xdabbad00]

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• I'm submitting a ...

  • 🪲 bug report

• What is the current behavior?
  I create an ECS task, and then try to create two CloudWatch Event rules to start that task, one as a schedule and one as an event pattern. If I create either of these independently it works, but if I try to create both, it fails with:

./node_modules/@aws-cdk/core/lib/construct.ts:496
      throw new Error(`There is already a Construct with name '${childName}' in ${typeName}${name.length > 0 ? ' [' + name + ']' : ''}`);
            ^
Error: There is already a Construct with name 'PutTargets' in FargateTaskDefinition [taskDefinition]
    at ConstructNode.addChild (./node_modules/@aws-cdk/core/lib/construct.ts:496:13)
    at new ConstructNode (./node_modules/@aws-cdk/core/lib/construct.ts:143:18)
    at new Construct (./node_modules/@aws-cdk/core/lib/construct.ts:547:17)
    at new AwsCustomResource (./node_modules/@aws-cdk/custom-resources/lib/aws-custom-resource.ts:124:5)
    at EcsTask.bind (./node_modules/@aws-cdk/aws-events-targets/lib/ecs-task.ts:120:7)
    at Rule.addTarget (./node_modules/@aws-cdk/aws-events/lib/rule.ts:133:32)
    at new CloudmapperauditorStack (./lib/cloudmapperauditor-stack.js:121:10)
    at Object.<anonymous> (./bin/cloudmapperauditor.js:9:1)
    at Module._compile (internal/modules/cjs/loader.js:734:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:745:10)

An example code snippet is:

  var ecs_target = new targets.EcsTask({cluster: cluster, taskDefinition: taskDefinition});

    // Create rule to trigger this be run every 24 hours
    new events.Rule(this, "scheduled_run", {
      ruleName: "cloudmapper_scheduler",
      // Run at 2am EST (6am UTC) every night
      schedule: events.Schedule.expression("cron(0 6 * * ? *)"),
      description: "Starts the CloudMapper auditing task every night",
      targets: [ecs_target]
    });

    // Create rule to trigger this manually
    new events.Rule(this, "manual_run", {
      ruleName: "cloudmapper_manual_run",
      eventPattern: {source: ['cloudmapper']},
      description: "Allows CloudMapper auditing to be manually started",
      targets: [ecs_target]
    });

I don't know if this impacts resources other than ECS tasks. Commenting out the line for targets: [ecs_target] in either place allows this to run successfully, but the code above will fail with the error message above.

• What is the expected behavior (or behavior of feature suggested)?
  I would like to be able to create two CloudWatch Rules, that each trigger the same target.

• What is the motivation / use case for changing the behavior or adding this feature?
  I want to be able to run my ECS task on a schedule, but also be able to kick it off manually for testing or other needs.

• Please tell us about your environment:

  • CDK CLI Version: 1.2.0
  • OS: OSX
  • Language: TypeScript

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. associated pull-request, stackoverflow, gitter, etc)