Can Client-Go Watch CustomResourceDefinitions (CRDs)?

Watching CustomResourceDefinitions (CRD) with Client-Go

In Kubernetes, it is crucial to monitor newly created or modified resources, including CustomResourceDefinitions (CRDs). While simple Rest Clients can handle this task, the question arises: can client-go, the official Kubernetes client library, fulfill this role for CRDs?

The Challenge: Client-Go's Lack of CRD Awareness

Client-go provides built-in support for standard Kubernetes resources such as pods and services. However, CRDs are custom-defined resources not natively known to client-go. As a result, using client-go to monitor CRDs requires addressing this recognition gap.

Solution: Custom Client Generation for CRDs

The solution lies in generating a custom client for the CRD. Kubernetes offers code-generation tools that allow developers to define the structures of the CRD API and automatically generate the necessary client. By doing so, client-go gains the ability to recognize and interact with the CRDs.

Sample Controller and Code Generation Tools

Kubernetes provides a sample-controller example that demonstrates how to watch for CRDs using client-go. The pkg directory in this example contains the generated API definitions and client code, while the main.go and controller.go files handle the watching and processing of CRD events.

Simplified Code Generation with Kubebuilder

Recently, kubebuilder, a tool maintained by kubernetes-sigs, has emerged as a convenient way to generate client configurations and controllers for CRDs. With kubebuilder, developers can streamline the process of monitoring CRDs using client-go.

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