Kustomize

Plain YAML customization: no templating; patch-based overlays. Built into kubectl (kubectl apply -k).

• Structure: base/ (shared) + overlays/ (env-specific patches)

kustomization.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
- deployment.yaml
- service.yaml

namePrefix: prod-

commonLabels:
  env: production

commonAnnotations:
  team: platform

images:
- name: nginx
  newTag: "1.26"
- name: myapp
  newName: registry.io/myapp
  newTag: "2.0"

patches:
- path: patch-replicas.yaml      # separate file
- patch: |                       # inline patch
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: webapp
    spec:
      replicas: 5

JSON 6902 patch (precise field targeting)

patches:
- target:
    kind: Deployment
    name: webapp
  patch: |
    - op: replace
      path: /spec/replicas
      value: 5
    - op: add
      path: /spec/template/spec/containers/0/env/-
      value:
        name: ENV
        value: production

Bases and overlays

# overlays/prod/kustomization.yaml
resources:
  - ../../base
  - grafana-depl.yaml
namespace: dev
namePrefix: dev-

configMapGenerator and secretGenerator

configMapGenerator:
- name: app-config
  literals:
  - DB_HOST=mysql
  - DB_PORT=3306
  files:
  - app.properties

secretGenerator:
- name: db-secret
  literals:
  - password=s3cr3t

• Generated name: app-config-<hash>; reference by base name; Kustomize rewrites refs automatically
• Suppress hash (not recommended): options: {disableNameSuffixHash: true}

Commands

kustomize build k8s/overlays/dev      # if kustomize CLI installed

Helm vs Kustomize

Exam gotchas

• Every kustomize dir needs kustomization.yaml
• Overlay references base via resources: - ../../base
• images transformer changes tags without editing deployment YAML
• configMapGenerator / secretGenerator appends hash: reference by base name
• Strategic merge patch: specify only what changes; K8s merges with existing spec
• JSON 6902: precise op-based (add/replace/remove); use strategic merge for most exam scenarios