Kustomize Has a Free API: Template-Free Kubernetes Configuration

Why Kustomize

Kustomize customizes Kubernetes YAML without templates — no Go templating, no Helm charts. Overlay base configs with patches for different environments.

Built into kubectl

kubectl apply -k overlays/production/

Base Configuration

# base/kustomization.yaml
resources:
  - deployment.yaml
  - service.yaml

# base/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 1
  template:
    spec:
      containers:
        - name: app
          image: myorg/myapp:latest
          resources:
            limits:
              memory: 256Mi

Production Overlay

# overlays/production/kustomization.yaml
bases:
  - ../../base

replicas:
  - name: myapp
    count: 5

images:
  - name: myorg/myapp
    newTag: v2.0.0

patchesStrategicMerge:
  - increase-resources.yaml

namePrefix: prod-
namespace: production

labels:
  - pairs:
      environment: production

# overlays/production/increase-resources.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    spec:
      containers:
        - name: app
          resources:
            limits:
              memory: 1Gi
              cpu: "1"

Common Transformers

# kustomization.yaml
configMapGenerator:
  - name: app-config
    literals:
      - DB_HOST=postgres
      - DB_PORT=5432

secretGenerator:
  - name: app-secrets
    literals:
      - DB_PASSWORD=secret

commonLabels:
  app: myapp
  team: backend

Key Features

• No templates — plain YAML, no Go/Jinja syntax
• Overlays — base + patches per environment
• Built into kubectl — no extra tools needed
• Generators — ConfigMaps and Secrets from files/literals
• Transformers — labels, annotations, namespace, prefix
• Composable — combine multiple bases

Resources

• Kustomize Docs
• GitHub

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