Custom resources, which were first introduced in Kubernetes 1.7, were designed as an extension point to let users create custom API objects and act as native Kubernetes objects. This was done so that users could extend Kubernetes to support the custom objects for their application or specific use cases. Custom resources can be dynamically registered and unregistered. There are two ways to create custom resources: by using a CRD or aggregated API. CRDs are much easier, while an aggregated API requires additional coding in Go. In this section, we'll learn how to write a CRD from scratch.