Generic k8s resource client

[hongchaodeng]

Currently when we use client-go per resource API, it requires to use pick specific gvk. For example:

kubecli.CoreV1().Services(ns).Create(svc)

In the SDK, we can't pick a client for the GroupVersionKind (GVK) of objects output from the handler. Even though we can hardcode predefined k8s APIs, there are unknown custom resource GVKs.

This is actually the same problem that kubectl has -- how does kubectl know about custom resource?

Create this issue to collect discussion.

[hongchaodeng]

(Actually k8s GC code is a better example.)

We can use dynamic client which is able to work with any resource object.

Creating dynamic client:
https://github.com/kubernetes/kubernetes/blob/11ecad262939c72404b592e721f172f1dac352dd/cmd/kube-controller-manager/app/core.go#L354-L381

Creating resource client from dynamic client at runtime:
https://github.com/kubernetes/kubernetes/blob/11ecad262939c72404b592e721f172f1dac352dd/pkg/controller/garbagecollector/garbagecollector.go#L287