Custom Resources and Operators

Cluster Architecture and Configuration / Guide 20 of 103 / Intermediate

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 35 min

apiextensions.k8s.io/v1 requires a structural schema, so the permissive CRDs from older tutorials no longer apply cleanly.

• CRD APIapiextensions.k8s.io/v1

This guide includes

Use this when you need to know what a CRD gives you and where an operator has to take over. This matters because a CustomResourceDefinition buys a real Kubernetes resource - validation, RBAC, kubectl support - and no behaviour whatsoever.

• adding an entire resource type to the API server with one YAML file
• creating and listing instances that behave exactly like built-in resources
• watching the API server reject an object that violates the schema
• splitting status from spec with the status subresource, and patching it separately
• confirming nothing happens without an operator, then deleting the CRD and taking every object with it

Before you start

• The API objects and kubectl guides.
• The RBAC guide, since custom resources need their own rules.
• Cluster-admin, because creating a CRD changes the cluster's API surface.

1. 1

   One YAML file adds a resource type

2. 2

   It behaves like a built-in resource

3. 3

   Validation is enforced by the API server

4. 4

   The status subresource, and why it is separate

5. 5

   Nothing happens, and that is the whole point of an operator

6. 6

   Deleting the CRD deletes every object of that kind

Official sources

• Custom Resources
• CustomResourceDefinitions
• Operator pattern
• CRD validation rules (CEL)
• Finalizers