(aws-ec2): ApplicationLoadBalancer - Expose created Listeners as collection

Listeners that are created via calls to addListener() should be exposed as a collection property of ApplicationLoadBalancer.

Use Case

When the ALB is created through mechanisms outside of my direct control, such as ApplicationLoadBalancedFargateService, I am unable to alter listener properties such as the sslPolicy (see https://github.com/aws/aws-cdk/issues/8816).

Proposed Solution

There is a general OO design principal that goes something like “that which creates contains”. (At least according to Craig Larman there is). This principal seems to be followed generally throughout the CDK but seems to have been missed in this instance.

Add a public Listeners property which includes listeners that were added via addListeners.

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

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This is a 🚀 Feature Request

[rcollette]

I have to remember with Typescript that the goto method of overriding behavior is not necessarily Monkey Patching. Inheritance works.

I would still classify this as a workaround.

/**
 * An ApplicationLoadBalancer whose listener ssPolicy is set to SslPolicy.FORWARD_SECRECY_TLS12
 *
 * <p>The default ApplicationLoadBalancer sslPolicy is set to include TLS 1.1 and static ciphers.</p>
 * <p>ApplicationLoadBalancer's constructor properties do not include an option for specifying the default sslPolicy
 * used when the addListener method is called by other constructs such as ApplicationLoadBalancedFargateService and
 * it also does not expose the listeners collection as a property so that the sslPolicy can be modified after the
 * fact.</p>
 * <p>We use this class to provide a means of consistently set the TLS version to corporate standards when using an ALB.</p>
 */
export class ApplicationLoadBalancerStandardized extends ApplicationLoadBalancer {

    public addListener(id: string, props: BaseApplicationListenerProps): ApplicationListener {
        // HACK: cast to any so we can override a "readonly" property.
        (props.sslPolicy as any) = SslPolicy.FORWARD_SECRECY_TLS12;
        return super.addListener(id, props);
    }
}

In use

// We create the ALB explicitly rather than letting ApplicationLoadBalancedFargateService (ALBFS)
// create it so that we can set the sslPolicy, which is not possible when the ALB is created with ALBFS.
// To match the ALB id that would be generated by ALBFS if it were to create the ALB, we must prefix
// the ALB id with the same id as the ALBFS.
const loadBalancer = new ApplicationLoadBalancerStandardized(this, `${this._props.serviceName}LB`, {
  vpc: cluster.vpc,
  internetFacing: this._props.publicLoadBalancer !== undefined ? this._props.publicLoadBalancer : true
});
const fargateService = new ApplicationLoadBalancedFargateService(this, this._props.serviceName, {
  cluster,
  loadBalancer,
  ...
  ...

[MisterGlass]

I have this exact use case as well. Is there any timeline on a fix? I may have to rewrite my whole stack to allow setting this.