Kustomize

Manage multi-environment deployments using Kustomize overlays.

Time: ~10 minutes Difficulty: Intermediate

What You Will Learn

• Base + overlay pattern for DRY configuration
• Environment-specific patches (replicas, resources, env vars)
• Kustomize name prefixes and namespace scoping
• ConfigMap generation from files

Deploy

Navigate to the demo directory:

cd demos/kustomize

Deploy the development overlay:

kubectl apply -k overlays/development/

Deploy the production overlay:

kubectl apply -k overlays/production/

Verify

# Development
kubectl get pods -n kustomize-dev
kubectl port-forward svc/dev-nginx-service 8081:80 -n kustomize-dev

# Production
kubectl get pods -n kustomize-prod
kubectl port-forward svc/prod-nginx-service 8082:80 -n kustomize-prod

Open http://localhost:8081 for the dev page (orange) and http://localhost:8082 for the prod page (green).

What is Happening

base/                          # Shared configuration
  deployment.yaml              # 3 replicas, health checks, resource limits
  service.yaml                 # ClusterIP on port 80
  configmap.yaml               # nginx config + landing page
  kustomization.yaml           # Ties it together

overlays/
  development/                 # Dev-specific overrides
    kustomization.yaml         # 2 replicas, dev- prefix, lower resources
    deployment-patch.yaml      # Smaller CPU/memory limits
    ingress.yaml               # nginx-dev.local hostname
    index.html                 # Orange-themed landing page

  production/                  # Prod-specific overrides
    kustomization.yaml         # 5 replicas, prod- prefix, higher resources
    deployment-patch.yaml      # Larger CPU/memory limits
    ingress.yaml               # nginx-prod.local hostname
    index.html                 # Green-themed landing page

Both environments share the same base manifests. Overlays only specify what differs: replica count, resource limits, namespace, and visual theme.

Experiment

1. Preview what Kustomize generates without applying:

   kubectl kustomize overlays/development/

2. Compare the two environments:

   diff <(kubectl kustomize overlays/development/) \
        <(kubectl kustomize overlays/production/)

3. Add a new environment (e.g., staging) by creating a new overlay directory:

   cp -r overlays/development/ overlays/staging/

   Then edit kustomization.yaml to set a different namespace, prefix, and replica count.

Cleanup

kubectl delete namespace kustomize-dev kustomize-prod

Further Reading

See docs/deep-dive.md for a detailed explanation of the base+overlay model, configMapGenerator internals, strategic merge patches vs JSON patches, and how to build a staging overlay from scratch.

Next Step

Move on to ArgoCD to automate deployments with GitOps.