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Curriculum 22: Custom Resources & CRDs

Working with Custom Resources

15 min · 35 XP

Working with Custom Resources

Once a CRD is registered in your cluster, you can create and manage custom resources (CRs) using the same kubectl commands you use for built-in resources like Pods and Deployments.

Creating a Custom Resource

Given a CRD for CronTab in the stable.example.com group:

apiVersion: stable.example.com/v1
kind: CronTab
metadata:
  name: my-cron-job
  namespace: default
spec:
  cronSpec: "*/5 * * * *"
  image: my-cron-image:latest
  replicas: 3

# Apply the custom resource
kubectl apply -f my-crontab.yaml

Listing CRDs in the Cluster

# See all registered CRDs
kubectl get crd

# Output:
# NAME                          CREATED AT
# crontabs.stable.example.com   2025-01-15T10:30:00Z
# certificates.cert-manager.io  2025-01-10T08:00:00Z

# Get details about a specific CRD
kubectl describe crd crontabs.stable.example.com

Querying Custom Resources

Once created, custom resources work just like any other resource type:

# List all CronTab resources
kubectl get crontabs
kubectl get ct          # using the short name

# Output with additionalPrinterColumns:
# NAME          SCHEDULE      REPLICAS   AGE
# my-cron-job   */5 * * * *   3          2m

# Get detailed YAML output
kubectl get ct my-cron-job -o yaml

# Describe a custom resource
kubectl describe ct my-cron-job

# Get custom resources across all namespaces
kubectl get ct -A

Editing and Deleting

# Edit a custom resource
kubectl edit ct my-cron-job

# Patch a field
kubectl patch ct my-cron-job \
  --type=merge \
  -p '{"spec":{"replicas":5}}'

# Delete a custom resource
kubectl delete ct my-cron-job

Key Takeaways

  • Custom resources use the same kubectl verbs as built-in resources: get, describe, edit, delete
  • Short names defined in the CRD work everywhere
  • kubectl get crd lists all registered custom resource types in the cluster
  • Custom resources are validated against the schema defined in their CRD