feat: Add examples for kustomize

Signed-off-by: Abhishek Veeramalla <abhishek.veeramalla@gmail.com>

Author: iam-veeramalla

01-basics/README.md

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+# Kustomize Basics
+
+## What You'll Learn
+In this section, you'll learn the fundamental concepts of Kustomize:
+- How to organize your Kubernetes configurations
+- How to make simple changes without touching the original files
+- Understanding base and overlay structure
+
+## Directory Structure
+```
+.
+├── base/                  # Your original configuration
+│   ├── deployment.yaml    # A basic nginx deployment
+│   └── kustomization.yaml # Tells Kustomize what to include
+└── overlay/              # Your customizations
+    └── kustomization.yaml # Defines how to modify the base
+```
+
+## Understanding the Files
+
+### Base Configuration
+The `base/` directory contains your original, unchanged configuration:
+- `deployment.yaml`: A simple nginx web server deployment
+- `kustomization.yaml`: Lists which files to include
+
+### Overlay Configuration
+The `overlay/` directory shows how to customize the base:
+- Adds a prefix to all resources (`dev-`)
+- Updates the nginx image version to 1.20
+- Adds environment labels
+
+## Try It Yourself
+
+1. View the base deployment:
+```bash
+kubectl kustomize base/
+```
+
+2. View the customized version:
+```bash
+kubectl kustomize overlay/
+```
+
+3. Apply to your cluster:
+```bash
+kubectl apply -k overlay/
+```
+
+## What's Happening?
+1. Kustomize reads the base configuration
+2. It applies the changes specified in the overlay:
+   - Adds "dev-" prefix to names
+   - Updates the nginx image
+   - Adds environment labels
+3. Generates the final configuration
+
+## Key Concepts
+- **Base**: Your original configuration
+- **Overlay**: Your customizations
+- **kustomization.yaml**: Tells Kustomize what to do
+- **Resources**: The Kubernetes files you want to modify

01-basics/base/deployment.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: web-app
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: web-app
+  template:
+    metadata:
+      labels:
+        app: web-app
+    spec:
+      containers:
+      - name: web-app
+        image: nginx:1.19
+        ports:
+        - containerPort: 80

01-basics/base/kustomization.yaml

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+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+- deployment.yaml

01-basics/overlay/kustomization.yaml

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+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namePrefix: dev-
+resources:
+- ../base
+
+images:
+- name: nginx
+  newName: nginx
+  newTag: "1.20"
+
+commonLabels:
+  environment: development

02-patches/README.md

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+# Working with Patches in Kustomize
+
+## What You'll Learn
+This section teaches you how to make specific changes to your Kubernetes resources using patches:
+- Strategic Merge Patches: Easy way to modify configurations
+- JSON 6902 Patches: More precise modifications
+- When to use each type of patch
+
+## Directory Structure
+```
+.
+├── base/                  # Original configuration
+│   └── deployment.yaml    # Basic deployment with resource limits
+└── overlay/              # Your modifications
+    ├── increase-memory.yaml    # Strategic merge patch
+    ├── add-label.yaml         # JSON patch
+    └── kustomization.yaml     # Combines both patch types
+```
+
+## Understanding Patches
+
+### Strategic Merge Patch
+- File: `increase-memory.yaml`
+- Purpose: Updates memory limit from 128Mi to 256Mi
+- How it works: Overlays matching fields in the original
+- When to use: For simple modifications to existing fields
+
+### JSON 6902 Patch
+- File: `add-label.yaml`
+- Purpose: Adds a new label to the deployment
+- How it works: Specifies exact operations (add, remove, replace)
+- When to use: For precise changes or when working with arrays
+
+## Try It Yourself
+
+1. View the original deployment:
+```bash
+kubectl kustomize base/
+```
+
+2. See the patched version:
+```bash
+kubectl kustomize overlay/
+```
+
+## Key Concepts
+- **Strategic Merge Patch**: 
+  - Easier to write
+  - Works well with Kubernetes resources
+  - Good for simple changes
+  
+- **JSON 6902 Patch**:
+  - More precise control
+  - Can add/remove/replace specific values
+  - Better for complex changes
+
+## Common Use Cases
+1. Updating resource limits
+2. Adding labels or annotations
+3. Modifying container arguments
+4. Updating environment variables

02-patches/base/deployment.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: web-app
+spec:
+  replicas: 1
+  template:
+    spec:
+      containers:
+      - name: web-app
+        image: nginx:1.19
+        resources:
+          limits:
+            memory: "128Mi"
+            cpu: "100m"

02-patches/overlay/add-label.yaml

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+- op: add
+  path: /metadata/labels/app-type
+  value: web-server

02-patches/overlay/increase-memory.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: web-app
+spec:
+  template:
+    spec:
+      containers:
+      - name: web-app
+        resources:
+          limits:
+            memory: "256Mi"

02-patches/overlay/kustomization.yaml

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+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+- ../base
+
+patchesStrategicMerge:
+- increase-memory.yaml
+
+patchesJson6902:
+- target:
+    group: apps
+    version: v1
+    kind: Deployment
+    name: web-app
+  path: add-label.yaml

03-configmaps-secrets/README.md

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+# ConfigMaps and Secrets in Kustomize
+
+## What You'll Learn
+This section covers how to manage application configuration using Kustomize:
+- Creating ConfigMaps from files
+- Mounting ConfigMaps in pods
+- Updating configurations for different environments
+
+## Directory Structure
+```
+.
+├── base/                     # Base configuration
+│   ├── config/              # Configuration files
+│   │   └── app.properties   # Application properties
+│   ├── deployment.yaml      # Deployment using ConfigMap
+│   └── kustomization.yaml   # Generates ConfigMap
+└── overlay/                 # Environment-specific configs
+    ├── config/             
+    │   └── app.properties   # Modified properties
+    └── kustomization.yaml   # Updates ConfigMap
+```
+
+## Understanding the Setup
+
+### Base Configuration
+- `app.properties`: Default application settings
+- `deployment.yaml`: Mounts ConfigMap as a volume
+- `kustomization.yaml`: Generates ConfigMap from properties file
+
+### Overlay Configuration
+- Modified `app.properties` with environment-specific values
+- Uses `replace` behavior to update the entire ConfigMap
+
+## Try It Yourself
+
+1. View the base ConfigMap:
+```bash
+kubectl kustomize base/
+```
+
+2. See the modified version:
+```bash
+kubectl kustomize overlay/
+```
+
+## Key Features
+1. **ConfigMap Generation**
+   - Automatically creates ConfigMaps from files
+   - Handles updates and changes
+   - Generates unique names when content changes
+
+2. **Volume Mounting**
+   - Mounts ConfigMap as a volume
+   - Makes configuration available to containers
+   - Updates automatically when ConfigMap changes
+
+3. **Environment Overrides**
+   - Easy to maintain different configurations
+   - No need to duplicate entire files
+   - Clear separation of base and environment-specific settings
+
+## Best Practices
+1. Keep sensitive data out of ConfigMaps
+2. Use meaningful file names
+3. Document your configuration structure
+4. Version control your configurations