Lab: Create and Use a Custom Resource Definition (CRD)

Goal

Create a Fruit CRD that allows you to define fruits like apple, banana, etc., and deploy a controller that prints them.

Prerequisites

• Kubernetes cluster (e.g. Minikube)
• kubectl installed
• Optional: kustomize and controller-gen if building a full controller

Lab Structure

crd-lab/
├── crds/
│   └── fruit-crd.yaml
├── examples/
│   └── apple.yaml
└── controller/
    └── fruit-controller.sh

Define the CRD

📄 crds/fruit-crd.yaml

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: fruits.example.com
spec:
  group: example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                color:
                  type: string
                taste:
                  type: string
      subresources:
        status: {}
  scope: Namespaced
  names:
    plural: fruits
    singular: fruit
    kind: Fruit
    shortNames:
      - frt

Apply the CRD:

kubectl apply -f crds/fruit-crd.yaml

Create a Custom Resource (CR)

📄 examples/apple.yaml

apiVersion: example.com/v1
kind: Fruit
metadata:
  name: apple
spec:
  color: red
  taste: sweet

Apply the CR:

kubectl apply -f examples/apple.yaml

Verify:

kubectl get fruits
kubectl get fruit apple -o yaml

Create a Simple Controller (optional)

This is a demo controller (bash script) that watches the fruit CRs and prints them. In real apps you'd use a proper controller with client-go or Kubebuilder.

📄 controller/fruit-controller.sh

#!/bin/bash

echo "Watching for Fruit resources..."
kubectl get fruit --watch -o json | jq -c '.'

Run:

bash controller/fruit-controller.sh

Then try creating more fruits:

# examples/banana.yaml
apiVersion: example.com/v1
kind: Fruit
metadata:
  name: banana
spec:
  color: yellow
  taste: sweet

kubectl apply -f examples/banana.yaml

Clean Up

kubectl delete -f examples/
kubectl delete -f crds/

Summary