Kustomize

# Typical multi-env layout
k8s/
├── base/
│   ├── kustomization.yaml
│   ├── deployment.yaml
│   ├── service.yaml
│   └── configmap.yaml
└── overlays/
    ├── staging/
    │   ├── kustomization.yaml
    │   └── patch-replicas.yaml
    └── production/
        ├── kustomization.yaml
        ├── patch-replicas.yaml
        └── patch-resources.yaml

# base/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

namespace: my-app

namePrefix: prod-
nameSuffix: -v2

# commonLabels is deprecated — use labels (avoids mutating selectors)
labels:
  - pairs:
      app: my-app
      env: production
    includeSelectors: false

commonAnnotations:
  team: platform

resources:
  - deployment.yaml
  - service.yaml

images:
  - name: my-app
    newTag: v1.2.3

configMapGenerator:
  - name: app-config
    literals:
      - LOG_LEVEL=info
      - PORT=8080

# overlays/production/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ../../base

patches:
  - path: patch-replicas.yaml
  - path: patch-resources.yaml

images:
  - name: my-app
    newTag: v2.0.0

---
# patch-replicas.yaml (strategic merge patch)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 5

# More precise than strategic merge
# patch-resources.yaml
- op: replace
  path: /spec/template/spec/containers/0/resources/limits/memory
  value: "2Gi"

- op: add
  path: /spec/template/spec/containers/0/env/-
  value:
    name: EXTRA_VAR
    value: "true"

- op: remove
  path: /spec/template/spec/containers/0/livenessProbe

# Reference in kustomization.yaml
patches:
  - path: patch-resources.yaml
    target:
      kind: Deployment
      name: my-app

# Preview rendered output
kubectl kustomize ./overlays/production

# Apply overlay to cluster
kubectl apply -k ./overlays/production

# Delete resources defined in overlay
kubectl delete -k ./overlays/production

# Diff against live cluster
kubectl diff -k ./overlays/production

# Build with standalone kustomize CLI
kustomize build ./overlays/production

# Build and pipe to kubectl
kustomize build ./overlays/production \
  | kubectl apply -f -

# Generate ConfigMap from file
configMapGenerator:
  - name: app-config
    files:
      - config.properties
    options:
      disableNameSuffixHash: true

# Generate Secret from literals
secretGenerator:
  - name: db-creds
    literals:
      - DB_PASSWORD=secret123
    type: Opaque

# Replace image across all Deployments
images:
  - name: nginx
    newName: my-registry.example.com/nginx
    newTag: 1.27-alpine

# Add labels to all resources
labels:
  - pairs:
      managed-by: kustomize
      env: production
    includeSelectors: false