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CustomResourceDefinition: Add Your Own Kind

Part XII shifts from using Kubernetes to extending it. The first article is CustomResourceDefinition — declare a new kind of object, and the API server immediately serves it like a native resource: kubectl get works, it validates against a schema, it stores in etcd. We build a Widget CRD with type and value-range constraints, create a valid custom resource, watch two invalid ones get rejected, then update status through a separate subresource.