What is Kustomize in Kubernetes: Overview and Usage

Kustomize is a tool built into kubectl that helps you customize Kubernetes resource files without changing the original YAML. It lets you apply overlays and patches to base configurations, making it easier to manage different environments like development, testing, and production.

How It Works

Kustomize works like a recipe book for your Kubernetes YAML files. Instead of copying and editing the same files for each environment, you keep a base set of files and then create overlays that adjust only what needs to change. This is similar to having a basic pizza recipe and then adding different toppings for each occasion without rewriting the whole recipe.

It uses a kustomization.yaml file to list resources and specify changes like adding labels, changing image tags, or modifying configurations. When you run kubectl kustomize, it combines the base and overlays to produce the final YAML that Kubernetes applies.

Example

This example shows a base deployment and an overlay that changes the image tag for production.

yaml

base/deployment.yaml:
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: myapp:latest

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

overlays/production/kustomization.yaml:
resources:
- ../../base
images:
- name: myapp
  newTag: v1.2.3

Output

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: myapp:v1.2.3

When to Use

Use Kustomize when you want to manage Kubernetes configurations for multiple environments without duplicating files. It is perfect for teams that need to maintain a clean, DRY (Don't Repeat Yourself) setup where base configurations are shared and environment-specific changes are layered on top.

Common use cases include changing image tags for production, adding environment-specific labels or annotations, and modifying resource limits. It helps avoid errors from manual edits and keeps your deployment process consistent.

Key Points

• Kustomize is built into kubectl, so no extra installation is needed.
• It uses overlays to customize base YAML files without duplication.
• Supports patching, adding labels, changing images, and more.
• Helps manage multiple environments cleanly and safely.

Key Takeaways

Kustomize customizes Kubernetes YAML files without copying or editing the originals.

It uses a base and overlays system to manage environment-specific changes.

Built into kubectl, making it easy to use without extra tools.

Ideal for managing multiple environments like dev, test, and production.

Helps keep Kubernetes configurations clean, consistent, and error-free.