(ecs-patterns): omiting cluster and specifying only vpc results in an error

[madeline-k]

What is the problem?

The ecs-patterns README states that 'Instead of providing a cluster you can specify a VPC and CDK will create a new ECS cluster.' However, omiting the cluster prop and only provided a vpc results in an error. And there is not clear direction on how to do this properly.

So far I have noticed this issue with the following constructs. It might apply to more.

• NetworkMultipleTargetGroupsEc2Service
• ApplicationMultipleTargetGroupsEc2Service
• ApplicationLoadBalancedEc2Service

This might just be a miss in the documentation, and not missing functionality. I will need to dive deeper into this to find out.

Reproduction Steps

Synthesize and app with this sample code:

    const stack = new Stack();
    const vpc = new Vpc(stack, 'VPC');

    const service = new ApplicationMultipleTargetGroupsEc2Service(stack, 'Service', {
      vpc,
      memoryLimitMiB: 1024,
      taskImageOptions: {
        image: ContainerImage.fromRegistry('test'),
      },
    });

What did you expect to happen?

No errors, and it synthesizes an ECS service with a cluster created by the CDK.

What actually happened?

I get this error:

      [Default/Service/Service] Cluster for this service needs Ec2 capacity. Call addXxxCapacity() on the cluster.

CDK CLI Version

1.139.0

Framework Version

No response

Node.js Version

12.22.7

OS

MacOS

Language

Typescript

Language Version

No response

Other information

No response

[michaeldrey]

This looks like an issue with the getDefaultCluster function here.

  protected getDefaultCluster(scope: Construct, vpc?: IVpc): Cluster {
    // magic string to avoid collision with user-defined constructs
    const DEFAULT_CLUSTER_ID = `EcsDefaultClusterMnL3mNNYN${vpc ? vpc.node.id : ''}`;
    const stack = cdk.Stack.of(scope);
    return stack.node.tryFindChild(DEFAULT_CLUSTER_ID) as Cluster || new Cluster(stack, DEFAULT_CLUSTER_ID, { vpc });
  }

The new Cluster declaration is a valid reference if we were creating a fargateService, which is probably why it wasn't caught till runtime; however, since we're creating an Ec2 service we need to specify the capacity type which honestly leads into a bigger discussion as we would need to pass in an ASG and ASG provider.

This function is repeated in all base ec2 constructs. I'll keep digging into this

[XTEKiyZRLr8UsiQN]

+1, this construct is unusable without a provided cluster. It seems like the intent was to use capacity_provider_strategies but that is not in use right now.