Kustomize - Configuration Management

Kustomize is a template-free configuration management tool for Kubernetes. It helps you organize and customize Kubernetes YAML files without duplicating code.

Overview

Kustomize provides:

• Base Configurations - Common manifests shared across environments
• Overlays - Environment-specific patches (staging, production)
• Resource Patching - Modify resources without copying entire files
• Template-Free - No new programming language to learn

Key Concepts

Base

The base/ directory contains the common configuration that all environments share.

Overlays

The overlays/ directory contains environment-specific patches that modify the base.

How It Works

1. Define base configuration
2. Create overlays for each environment
3. Kustomize merges base + overlay
4. Output final YAML for deployment

Usage

Build Configuration

# Build staging configuration
kubectl kustomize kustomize/overlays/staging

# Build production configuration
kubectl kustomize kustomize/overlays/production

# Apply directly
kubectl apply -k kustomize/overlays/staging

Common Operations

# Preview changes
kubectl kustomize kustomize/overlays/staging

# Validate
kubectl kustomize kustomize/overlays/staging --dry-run=client

# Apply
kubectl apply -k kustomize/overlays/staging

Base Structure

base/
├── kustomization.yaml    # Base configuration
├── deployment.yaml      # Common deployment
├── service.yaml         # Common service
└── configmap.yaml       # Common config

Overlay Structure

overlays/
├── staging/
│   ├── kustomization.yaml    # References base + patches
│   └── patches/
│       └── resource-limits.yaml
└── production/
    ├── kustomization.yaml
    └── patches/
        └── resource-limits.yaml

Examples

Base Kustomization

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

resources:
  - deployment.yaml
  - service.yaml
  - configmap.yaml

commonLabels:
  app: sample-app
  managed-by: kustomize

Staging Overlay

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

bases:
  - ../../base

replicas:
  - name: sample-app
    count: 2

patches:
  - path: patches/resource-limits.yaml

namespace: staging

Production Overlay

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

bases:
  - ../../base

replicas:
  - name: sample-app
    count: 5

patches:
  - path: patches/resource-limits.yaml

namespace: production

Best Practices

1. Keep base minimal - Only common configurations
2. Use overlays for differences - Environment-specific changes
3. Version control everything - Base and overlays in Git
4. Test builds - Always preview before applying

Additional Resources

• Kustomize Documentation
• Kustomize Tutorial