AWS::ECS::Service needs DependsOn AWS::ElasticLoadBalancingV2::ListenerRule

[nathanpeck]

22/26 | 10:15:33 | CREATE_FAILED        | AWS::ECS::Service                         | greeting-service/Service (greetingserviceService8DA58640) The target group with targetGroupArn arn:aws:elasticloadbalancing:us-east-1:209640446841:targetgroup/greet-inter-7A1DWCFAH8FU/c4bab708f6cad935 does not have an associated load balancer. (Service: AmazonECS; Status Code: 400; Error Code: InvalidParameterException; Request ID: f6e72ff4-e756-11e8-afbf-dd214588018c)

When creating a service and adding it to a load balancer the CloudFormation template fails to deploy with the above error. Example code:

const greeterService = new ecs.Ec2Service(this, 'greeter-service', {
      cluster: cluster,
      desiredCount: 2,
      taskDefinition: greeterTaskDefinition
    });

     // Internet facing load balancer for the frontend services
    const externalLB = new elbv2.ApplicationLoadBalancer(this, 'external', {
      vpc: vpc,
      internetFacing: true
    });

    const externalListener = externalLB.addListener('PublicListener', { port: 80, open: true });

    externalListener.addTargets('greeter', {
      port: 80,
      targets: [greeterService]
    });

This is probably happening because the AWS::ECS::Service resource needs a DependsOn to the AWS::ElasticLoadBalancingV2::ListenerRule resource. Otherwise it is a race condition that causes a failure if the service resource creation starts before the listener rule is ready.

[rix0rrr]

Edit: ah no, you're right.

[RafeArnold]

Not sure if it will be seen here, but I don't understand why the service would have to depend on any of the other declared resources (load balancer, listener, target group). Surely the service can exist independently of any of these other resources, and rather should be a dependency of the other resources?

I'm bringing this up because I want to conditionally create a load balancer and target group containing a service that will always exist, but CloudFormation cannot construct the service when the load balancer isn't created because the service depends on the load balancer listener. When I don't add the load balancer and target group ever (i.e. don't declare them at all), the service can be created just fine.