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.

[dcaruso-pathpoint]

I am not sure why this is needed either.

The NLB or ALB and ECS Service should be allowed to create in parallel.

The target group evaluates LB health checks correct?

Only the Target group should be waiting on creation of the ECS Service and LB?

[nathanpeck]

At the time I opened this issue the Amazon ECS service attempted to communicate with the load balancer and target group as part of the service setup process therefore the load balancer and target group must already exist prior to the service being created. Years later we added the ability for an ECS service to start out with no LB or target group and add one later. However, in terms of CloudFormation it would still be better to just procreate the dependency resources and create the ECS service once rather than creating the service and then updating it to use the LB and target group

…

On Fri, Feb 14, 2025 at 1:57 PM Daniel Caruso II ***@***.***> wrote: I am not sure why this is needed either. The NLB or ALB and ECS Service should be allowed to create in parallel. The target group evaluates LB health checks correct? Only the Target group should be waiting on creation of the ECS Service and LB? — Reply to this email directly, view it on GitHub <#1160 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA2VN6RBPGRXPKCGVJUSZ6L2PY4A3AVCNFSM6AAAAABMUDOC2OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNRQGA2TGNRWGU> . You are receiving this because you authored the thread.Message ID: ***@***.***> [image: dcaruso-pathpoint]*dcaruso-pathpoint* left a comment (aws/aws-cdk#1160) <#1160 (comment)> I am not sure why this is needed either. The NLB or ALB and ECS Service should be allowed to create in parallel. The target group evaluates LB health checks correct? Only the Target group should be waiting on creation of the ECS Service and LB? — Reply to this email directly, view it on GitHub <#1160 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA2VN6RBPGRXPKCGVJUSZ6L2PY4A3AVCNFSM6AAAAABMUDOC2OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNRQGA2TGNRWGU> . You are receiving this because you authored the thread.Message ID: ***@***.***>