Exercise

  1. Create a directory structure for a Kustomize project with:

    • a base layer
    • a development and a production overlays

  2. Create resources in the base layer:

    • A Deployment named webapp using nginx:1.26 image with 2 replicas
    • A Service named webapp-service exposing port 80

  3. Create a kustomization.yaml file in the base directory that references both resources

  4. Apply the base configuration

  5. Configure the development overlay:

    • Changes the image to nginx:1.28
    • Adds a env: development label to all resources
    • Sets the replica count to 1

  6. Preview the development overlay using kubectl kustomize without applying

  7. Apply the development overlay

  8. Create a production overlay that:

    • Changes the image to nginx:1.28-alpine
    • Adds a env: production label to all resources
    • Sets the replica count to 5
    • Changes the service type to LoadBalancer

  9. Preview the production overlay

  10. Apply the production overlay

  11. Verify the production changes

  12. Delete the resources

Documentation

https://kubectl.docs.kubernetes.io/guides/introduction/kustomize/


Solution
  1. Create a directory structure for the Kustomize project
mkdir -p base
mkdir -p overlays/development
mkdir -p overlays/production
  1. Create resources in the base layer:

Create the following specifications in the base folder:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 2
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: webapp
        image: nginx:1.26
        ports:
        - containerPort: 80
apiVersion: v1
kind: Service
metadata:
  name: webapp-service
spec:
  selector:
    app: webapp
  ports:
  - port: 80
    targetPort: 80
  type: ClusterIP
  1. Create a kustomization.yaml file in the base directory that references both resources
kustomization.yaml
resources:
- deployment.yaml
- service.yaml
  1. Apply the base configuration
$ kubectl apply -k base
service/webapp-service created
deployment.apps/webapp created
  1. Configure the development overlay:

In the overlays/development folder, create the following kustomization.yaml file:

kustomization.yaml
resources:
- ../../base

labels:
- pairs:
    env: development

patches:
- patch: |-
    - op: replace
      path: /spec/template/spec/containers/0/image
      value: nginx:1.28
    - op: replace
      path: /spec/replicas
      value: 1
  target:
    kind: Deployment
    name: webapp

This file specifies:

  • the base resources to use
  • the labels to add
  • the patches that need to be applied to the base resources to change the image and the number of replicas
ℹī¸

Instead of defining the patches in the kustomization file, we could also create the deployment-patch.yaml file in the overlays/development:

deployment-patch.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 1
  template:
    spec:
      containers:
      - name: webapp
        image: nginx:1.28

And update the kustomization.yaml, so it applies this patch:

kustomization.yaml
resources:
- ../../base

labels:
- pairs:
    env: development

patches:
- deployment-patch.yaml
  1. Preview the development overlay:

kubectl has the kustomize built-in command for that purpose:

kubectl kustomize overlays/development

You should see the resulting Deployment’s specification is now based on nginx:1.28 and has 1 replica.

  1. Apply the development overlay:
$ k apply -k overlays/development           
service/webapp-service configured
deployment.apps/webapp configured
  1. Configure the production overlay

In the overlays/production folder, create the following kustomization.yaml file:

kustomization.yaml
resources:
- ../../base

labels:
- pairs:
    env: production

patches:
- patch: |-
    - op: replace
      path: /spec/template/spec/containers/0/image
      value: nginx:1.28-alpine
    - op: replace
      path: /spec/replicas
      value: 5
  target:
    kind: Deployment
    name: webapp
- patch: |-
    - op: replace
      path: /spec/type
      value: LoadBalancer
  target:
    kind: Service
    name: webapp-service
ℹī¸
As we’ve explained for the development overlay, we could also create external patches for both the Deployment and the Service instead of specifying the patches operation in the kustomization.yaml
  1. Preview the production overlay:
kubectl kustomize overlays/production
  1. Apply the production overlay:
kubectl apply -k overlays/production
  1. Verify the production changes:
ℹī¸
Since both overlays target the same resources, only the last applied configuration (production) is visible in the cluster. In real scenarios, you would deploy overlays to different namespaces.

Checking deployment:

kubectl get deployment webapp -o wide
kubectl get pods -l app=webapp

You should see 5 replicas running nginx:1.28-alpine.

Checking service:

kubectl get service webapp-service

You should see the Service type is now LoadBalancer.

Checking labels:

kubectl get deployment webapp --show-labels
kubectl get service webapp-service --show-labels

You should see the env: production label applied to both the Deployment and the Service.

  1. Clean up:
kubectl delete -k overlays/production
ℹī¸
This kustomization.yaml is a bit tricky; you’ll not have to create one from scratch in the CKA, but you need to understand Kustomize’s main concepts