feat(ecs): support availability zone rebalancing

[isker]

Issue # (if applicable)

Closes #32226

Reason for this change

New AZ rebalancing feature is not yet supported in L2 constructs.

Description of changes

Add availabilityZoneRebalancing to the props of FargateService and Ec2Service, and validate all the documented constraints on it being ENABLED.

Description of how you validated changes

Unit and integration tests.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.52%. Comparing base (f2ade56) to head (4b7ed11).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #32263   +/-   ##
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  Coverage   81.52%   81.52%           
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  Files         222      222           
  Lines       13715    13715           
  Branches     2417     2417           
=======================================
  Hits        11181    11181           
  Misses       2254     2254           
  Partials      280      280           

Flag	Coverage Δ
suite.unit	81.52% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	80.97% <ø> (ø)
packages/aws-cdk-lib/core	82.09% <ø> (ø)

[isker]

Hi @pahud, I saw you added an ecs-patterns-v2 label to #32226, which presumably means you want changes to those patterns to use this new feature as well. I have not implemented that here, at least not yet.

I have not used the patterns myself before, and when I took a look at them, I wasn't sure if I should default this feature to be enabled in services created by those patterns. What do you think?

[badmintoncryer]

Thank you for your contribution! I've made some comments.

[badmintoncryer]

I might not see many cases of overriding functions from a base class in CDK.
Perhaps it’s more common to define an interface in a base-service.ts file and have each subclass implement it. Please consider discussing this with the maintainers.

[isker]

attachToClassicLB is already on an interface, ILoadBalancerTarget:

aws-cdk/packages/aws-cdk-lib/aws-elasticloadbalancing/lib/load-balancer.ts

Lines 144 to 153 in 92d03e2

	/**
	* Interface that is going to be implemented by constructs that you can load balance to
	*/
	export interface ILoadBalancerTarget extends IConnectable {
	/**
	* Attach load-balanced target to a classic ELB
	* @param loadBalancer [disable-awslint:ref-via-interface] The load balancer to attach the target to
	*/
	attachToClassicLB(loadBalancer: LoadBalancer): void;
	}

aws-cdk/packages/aws-cdk-lib/aws-ecs/lib/base/base-service.ts

Lines 511 to 512 in 92d03e2

	export abstract class BaseService extends Resource
	implements IBaseService, elbv2.IApplicationLoadBalancerTarget, elbv2.INetworkLoadBalancerTarget, elb.ILoadBalancerTarget {

IIRC (I wrote this ~6 weeks ago 🌞) I had to disable this lint in order to be able to call super from the overriding methods. I need to call super because it refers to this private getter:

aws-cdk/packages/aws-cdk-lib/aws-ecs/lib/base/base-service.ts

Lines 1454 to 1458 in 92d03e2

	private get defaultLoadBalancerTarget() {
	return this.loadBalancerTarget({
	containerName: this.taskDefinition.defaultContainer!.containerName,
	});
	}

[aws-cdk-automation]

This PR has been in the MERGE CONFLICTS state for 3 weeks, and looks abandoned. To keep this PR from being closed, please continue work on it. If not, it will automatically be closed in a week.

[badmintoncryer]

I thought that by defining availabilityZoneRebalancing in BaseServiceOptions, all validations for maxHealthyPercent and those in attachToClassicLB() could be described in the BaseService class.
What do you think?

[isker]

BaseService is also extended by ExternalService, where AvailabilityZoneRebalancing is not a supported feature.

[badmintoncryer]

Thanks!

app.synth() in the integ test code is not necessary. Please remove those lines!

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 4b7ed11
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