ECS Cluster.addCapacity does not set autoscalingGroup property

When calling the ECS Cluster.addCapacity() method it does not actually set the “autoscalingGroup” property as expected:

Reproduction Steps

    // Create an ECS cluster
    this.cluster = new ecs.Cluster(this, 'Cluster', {
      vpc: this.vpc
    });

    // Add capacity to it
    this.cluster.addCapacity('greeter-capacity', {
      instanceType: new ec2.InstanceType('t3.xlarge'),
      minCapacity: 3,
      maxCapacity: 3
    });

    console.log(this.cluster.autoscalingGroup);

Expectation

According to the docs the expected output from the above code sample would be the construct for the autoscaling group that was created by addCapacity(): https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-ecs.Cluster.html#autoscalinggroup

However instead you just see “undefined”. This is because the getter for autoscalingGroup property uses an internal property which is only set in one place in the constructor: https://github.com/aws/aws-cdk/blob/master/packages/%40aws-cdk/aws-ecs/lib/cluster.ts#L116

If you do not specify capacity options at constructor time and instead choose to subsequently use the addCapacity() method then this property is never set within the addAutoscalingGroup() method, therefore the reference to the autoscaling group is not retrievable via the getter method as expected

Workarounds

You can specify capacity options as part of the constructor to get around this issue, instead of using addCapacity(). However, we should fix this so that addCapacity() sets the property correctly, as expected.

Environment

• CLI Version : 1.21.0
• Framework Version: 1.21.0

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This is 🐛 Bug Report

[gandroz]

My question is not really about the issue, but is kinda’ related. Is there any difference between using addCapacity or addAutoscalingGroup? I know that using addAutoscalingGroup I’ll need to create an ASG first. To me it seems that both methods do the same thing. Am I wrong?

As far as I understand it, addAutoscalingGroup adds an ASG already created to your cluster, whereas addCapacity creates an ASG under the hood, attaches it to the cluster and returns it so you can edit it. You have the same behavior when you use the console, you can choose to use an existing ASG or let ECS build one for you.

[github-actions[bot]]

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