CKAD — Kustomize Transformations

1 minute read

Common Kustomize Transformations

Kustomize provides many built-in transformations you can apply through kustomization.yaml:

# kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- deployment.yaml
- service.yaml

# Add a prefix to all resource names
namePrefix: myapp-

# Add a suffix to all resource names
nameSuffix: -v2

# Set namespace for all resources
namespace: production

# Add labels to all resources
commonLabels:
  team: backend
  env: prod

# Add annotations to all resources
commonAnnotations:
  managed-by: kustomize

# Change the image tag
images:
- name: myapp
  newTag: v3.0
  newName: registry.example.com/myapp

# Generate ConfigMaps
configMapGenerator:
- name: app-config
  literals:
  - DATABASE_HOST=postgres
  - DATABASE_PORT=5432

# Generate Secrets
secretGenerator:
- name: db-credentials
  literals:
  - username=admin
  - password=secret123

Transformation Summary

Transformation What It Does
namePrefix Adds prefix to all resource names
nameSuffix Adds suffix to all resource names
namespace Sets namespace for all resources
commonLabels Adds labels to all resources and selectors
commonAnnotations Adds annotations to all resources
images Overrides image names and tags
configMapGenerator Creates ConfigMaps from literals or files
secretGenerator Creates Secrets from literals or files

Strategic Merge Patches

For more complex modifications, use strategic merge patches. You write a partial YAML that gets merged with the base:

# overlays/prod/increase-resources.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api
spec:
  template:
    spec:
      containers:
      - name: api
        resources:
          requests:
            cpu: 500m
            memory: 512Mi
          limits:
            cpu: "1"
            memory: 1Gi

# overlays/prod/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- ../../base
patches:
- path: increase-resources.yaml

The patch is merged with the base resource by matching kind + metadata.name. Only the fields you specify are changed — everything else stays the same.

Helm vs Kustomize

Both tools help manage Kubernetes manifests, but they take different approaches:

Feature Helm Kustomize
Approach Templating Patching
Installation Separate binary Built into kubectl
Complexity Higher (Go templates) Lower (YAML patches)
Package sharing Charts + repositories Directories (git)
Rollback Built-in (helm rollback) Manual (re-apply old overlay)
Best for Third-party apps, complex deployments Environment-specific customization
CKAD focus Installing and managing charts Customizing with overlays

Exam tip: The CKAD may test both Helm and Kustomize. For Helm, focus on helm install, helm upgrade, helm rollback, and helm uninstall. For Kustomize, focus on kubectl apply -k and understanding kustomization.yaml.

Next: Hands-On Lab

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