CKAD — Kubernetes API
Extending Kubernetes
Kubernetes is extensible by design. You can define new resource types beyond the built-in Pods, Services, and Deployments. This lets teams model their own objects — databases, certificates, message queues — as native Kubernetes resources.
This chapter covers Custom Resource Definitions (CRDs) and the Operator pattern from the Application Environment, Configuration & Security domain.
Understanding the Kubernetes API
Before creating custom resources, understand how the API is structured.
API Groups and Versions
# List all API resources
kubectl api-resources | head -20
# List API resources for a specific group
kubectl api-resources --api-group=apps
# Check which API versions are available
kubectl api-versions | sort
Every resource belongs to an API group and has a version:
| Resource | API Group | Version |
|---|---|---|
| Pod | core (v1) | v1 |
| Deployment | apps | apps/v1 |
| Ingress | networking.k8s.io | networking.k8s.io/v1 |
| CronJob | batch | batch/v1 |
How kubectl Works with Resources
When you run kubectl get pods, kubectl:
- Discovers the API endpoint from the API server
- Sends a GET request to
/api/v1/namespaces/default/pods - The API server authenticates, authorizes, and returns data
Custom resources work the same way — once defined, kubectl treats them like built-in resources.
Next: Creating CRDs →
