Lab 17 - Kustomize overlays

Lab 17 - Kustomize overlays

Goal: one base, two environments, no copy-paste. Chapter: Kustomize

The base

# 1 -
mkdir -p ~/kust/base ~/kust/overlays/dev ~/kust/overlays/prod
cd ~/kust
kubectl create deploy web --image nginx:1.27 --dry-run=client -o yaml > base/deployment.yaml
kubectl create svc clusterip web --tcp 80:80 --dry-run=client -o yaml > base/service.yaml
cat > base/kustomization.yaml <<'YAML'
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - deployment.yaml
  - service.yaml
YAML
kubectl kustomize base

kubectl kustomize only renders - nothing is sent to the cluster.

Overlay: dev

# 2 -
cat > overlays/dev/kustomization.yaml <<'YAML'
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../../base
namespace: dev
namePrefix: dev-
labels:
  - pairs: { env: dev }
YAML
kubectl kustomize overlays/dev | grep -E 'name:|namespace:|env:'

Overlay: prod

# 3 -
cat > overlays/prod/kustomization.yaml <<'YAML'
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../../base
namespace: prod
labels:
  - pairs: { env: prod }
images:
  - name: nginx
    newTag: "1.28"
replicas:
  - name: web
    count: 3
configMapGenerator:
  - name: web-cfg
    literals:
      - LOG_LEVEL=warn
patches:
  - path: resources.yaml
YAML
cat > overlays/prod/resources.yaml <<'YAML'
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  template:
    spec:
      containers:
        - name: nginx
          resources:
            requests: { cpu: "50m", memory: "64Mi" }
            limits:   { memory: "128Mi" }
          envFrom:
            - configMapRef:
                name: web-cfg
YAML
kubectl kustomize overlays/prod

Find in the output: namespace prod, 3 replicas, image nginx:1.28, the resources from the patch, and a ConfigMap named web-cfg-<hash> - with the Deployment already pointing at the hashed name.

Apply both

# 4 -
kubectl create ns dev; kubectl create ns prod
kubectl apply -k overlays/dev
kubectl apply -k overlays/prod
kubectl get deploy,svc,cm -n dev
kubectl get deploy,svc,cm -n prod

# 5 - change config -> new hash -> automatic rollout
sed -i 's/LOG_LEVEL=warn/LOG_LEVEL=debug/' overlays/prod/kustomization.yaml
kubectl diff -k overlays/prod | grep -E '^[+-] ' | head
kubectl apply -k overlays/prod
kubectl rollout status deploy/web -n prod

With a plain ConfigMap you would need rollout restart (Lab 12). The hash suffix changes the Pod template, so the Deployment rolls by itself.

Discovery

Infodiscover

Task A. Add the label team: shop to every object in both environments by changing one file only.

Add to base/kustomization.yaml:

labels:
  - pairs: { team: shop }

kubectl apply -k overlays/dev && kubectl apply -k overlays/prod
kubectl get all -A -l team=shop

Task B. Give dev 2 replicas, without touching the base.

Add to overlays/dev/kustomization.yaml:

replicas:
  - name: web
    count: 2

Note: replicas refers to the name before namePrefix is applied.

Clean up

kubectl delete -k overlays/dev
kubectl delete -k overlays/prod
kubectl delete ns dev prod