feat: added construct for application ingress

[nemanja-kovacevic-thinkit]

ticket: https://techfromsage.atlassian.net/browse/PLT-651

This PR creates a new cdk8s construct for alb-application-ingress which contains all the logic and annotations required to allow sharing an ingress for a service and migrating traffic using weighting between namespaces.

[mrliptontea]

In other constructs, we call this selectorLabels because we use these labels for spec.selector.matchLabels. In case of Ingress, there is no such concept. But as we may still want to be able to add/override labels, I'd just call this - labels

Suggested change

	/**
	* Custom selector labels, they will be merged with the default app, role, and instance.
	* They will be applied to the workload, the pod and the service.
	* @default { app: "<app label from chart>", role: "server", instance: "<construct id>" }
	*/
	readonly selectorLabels?: { [key: string]: string };
	/**
	* Custom labels, they will be merged with the default app, role, and instance.
	* @default { app: "<app label from chart>", role: "server", instance: "<construct id>" }
	*/
	readonly labels?: { [key: string]: string };

Also, I think we'll need a separate props for app, and instance labels. Currently, the Ingress objects are created as part of the app's chart, but this construct will live in a separate chart that will be deployed into another namespace.

What we want to do here, is mirror the labels of the application's Pods, and the Service that exposes those Pods, labels.

For example, we have the following Service deployed to Persona's namespace:

apiVersion: v1
kind: Service
metadata:
  name: api-service
  namespace: persona-220728
  labels:
    app: persona
    canary: "false"
    environment: production
    instance: api
    managed-by: cdk8s
    region: eu
    role: server
    service: persona-eu

So in our Ingress chart, we want to be able to define an object that clearly points to the same thing:

new Ingress(this, `persona-api`, {
  app: "persona",     // <- we could create Ingresses for multiple apps in the same chart
  instance: "api",    // <- different from construct id above
  labels: {
    canary: "false",  // <- additional label for this case
  },
  hostnames: ["https://users.talis.com"],
  serviceRouting: [
    {
      namespace: "persona-220728",
      name: "api-service",
      port: 80,
      weight: 100,
    }
  ],
});

The service label can be created from app, environment, and region (we can skip watermark here):
https://github.com/talis/talis-cdk8s-constructs/blob/v4.8.0/lib/talis-chart/talis-chart.ts#L60

The end result should be an Ingress + external Service, created in the ingress namespace, with all the labels matching the Service shown above.

[mrliptontea]

I wonder if migration to this Ingress is also an opportunity to move away from certificate discovery, and just use cert ARNs. So maybe we should instead have a property for certificateArn

Suggested change

	/**
	* Domain name for TLS certificate discovery.
	* @see https://kubernetes-sigs.github.io/aws-load-balancer-controller/v2.3/guide/ingress/cert_discovery/
	*/
	readonly tlsDomain?: string | string[];
	/**
	* ARN of one or more certificate managed by AWS Certificate Manager
	*/
	readonly certificateArn?: string | string[];

[stephenrob]

Agree with this - makes moving certificates around a lot easier

[kiyanwang]

Ditto, makes sense!

[mrliptontea]

You can import the helpers already present in the library:
https://github.com/talis/talis-cdk8s-constructs/blob/526214c97af149ef673a3e957da4220d59f0fb76/lib/web-service/annotation-util.ts#L85-L92

You may move annotation-util.ts into lib/common/ directory.

[stephenrob]

Suggested change

	readonly ingressClassName: string;
	readonly ingressClassName: string;
	/**
	* Ingress class priority, between -1000 and 1000
	*/
	readonly ingressClassPriority: number;

This determines the relative order in the ingressClass of each ingress rules - should default to 0

[stephenrob]

For consistency these if blocks should use { ... } syntax for the blocks

[talisaspire]

🎉 This PR is included in version 4.9.0 🎉

The release is available on GitHub release

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