kustomize-overlays

# Kustomize Overlays

Master environment-specific Kubernetes configuration management using Kustomize overlays, strategic merge patches, and JSON patches for development, staging, and production environments.

## Overview

Overlays enable environment-specific customization of Kubernetes resources without duplicating configuration. Each overlay references a base configuration and applies environment-specific patches, transformations, and resource adjustments.

## Basic Overlay Structure

```
myapp/
├── base/
│   ├── kustomization.yaml
│   ├── deployment.yaml
│   ├── service.yaml
│   ├── configmap.yaml
│   └── ingress.yaml
└── overlays/
    ├── development/
    │   ├── kustomization.yaml
    │   ├── replica-patch.yaml
    │   └── namespace.yaml
    ├── staging/
    │   ├── kustomization.yaml
    │   ├── replica-patch.yaml
    │   ├── resource-patch.yaml
    │   └── namespace.yaml
    └── production/
        ├── kustomization.yaml
        ├── replica-patch.yaml
        ├── resource-patch.yaml
        ├── hpa.yaml
        └── namespace.yaml
```

## Base Configuration

### Base Kustomization

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

metadata:
  name: myapp-base

# Resources to include
resources:
  - deployment.yaml
  - service.yaml
  - configmap.yaml
  - ingress.yaml

# Common labels applied to all resources
commonLabels:
  app: myapp
  managed-by: kustomize

# Common annotations
commonAnnotations:
  version: "1.0.0"
  team: platform

# Name prefix for all resources
namePrefix: myapp-

# Default namespace (can be overridden in overlays)
namespace: default

# Image transformations
images:
  - name: myapp
    newName: registry.example.com/myapp
    newTag: latest
```

### Base Deployment

```yaml
# base/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec: