model: Introduce KubernetesResource interface

[ruromero]

Description of the change: Introduce KubernetesResource interface

Motivation for the change: This interface provides a simpler way to interact with metav1.Object and runtime.Object avoiding unnecessary type castings and more flexibility

func someFunc() {
	resources := []KubernetesResource{&corev1.Pod{}, &routev1.Route{}}
	iterateObjects(resources)
}

func iterateObjects(objects []KubernetesResource) {
	for _, o := range objects {
		doSomething(o)
		doSomethingElse(o)
	}
}

func doSomething(object runtime.Object) {
	//Do something
}

func doSomethingElse(object metav1.Object) {
	//Do something else
}

[estroz]

@ruromero are you using this interface in a controller? Can you provide a more detailed example of how you'd use this interface?

[ruromero]

@ruromero are you using this interface in a controller? Can you provide a more detailed example of how you'd use this interface?

Yes we use it extensively in different operators. e.g. https://github.com/kiegroup/kie-cloud-operator/blob/master/pkg/controller/kieapp/kieapp_controller.go#L199

This is actually part of our operator-utils library and wanted to contribute it to the operator-sdk. If you find it useful we can think of more utilities to contribute.

[camilamacedo86]

Why it should be added? What is the need/scenario that can be solved with?

[ruromero]

This can be an example where a generic method accepts any type of resource, sets the owner reference (metav1.Object) and creates the object (runtime.Object).

https://github.com/RHsyseng/operator-utils/blob/master/pkg/resource/write/writer.go#L62

[camilamacedo86]

I am not sure if we should add the OCP dep by default. wdyt @joelanford ?

[joelanford]

This is a duplicate of kubernetes-sigs/controller-runtime#594. Can we continue the discussion there?

[camilamacedo86]

After look the comment #2800 (comment) I understand that this suggestion would better addressed by via kubernetes-sigs/controller-runtime#594 as the solution applied there. So, I am closing this one.

However, please feel free to re-open if you think that it should still be addressed here or if I misunderstood something.

[ruromero]

Would you re-consider this PR if the issue in controller-runtime does not progress? I still believe this small interface would help many developers writing better operators/controllers.

[estroz]

@ruromero I would open this PR in controller-runtime. An implementation makes abstractions easier to discuss.