Introduction

In previous chapters, we learned about different Kubernetes objects, such as Pods, Deployments, and ConfigMaps. These objects are defined and managed by the Kubernetes API (that is, for these objects, the API server manages their creation and destruction, among other operations). However, you may want to extend the functions provided by Kubernetes to provide a feature that is not shipped with standard Kubernetes, and that cannot be enabled by the built-in objects provided by Kubernetes.

To build these functionalities on top of Kubernetes, we use Custom Resources (CRs). Custom Resource Definitions (CRDs) allow us to add a capability through which users can add custom objects to the Kubernetes server and use those CRs like any other native Kubernetes object. A CRD helps us to introduce our custom objects to the Kubernetes system. Once our CRD is created, it can be used like any other object in the Kubernetes server. Not only that, but we can also use the Kubernetes API...