## From "Hello World" to Kubernetes: An End-to-End Guide

## From "Hello World" to Kubernetes: An End-to-End Guide

This article will guide you through the process of taking a simple "Hello World" Spring Boot application, containerizing it with Docker, automating the build and push process using GitHub Actions (including the crucial step of using secrets), and finally, making it ready for deployment on Kubernetes.

### 1. Crafting the "Hello World" Spring Boot Application

```java

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RestController;

@RestController

public class HelloController {

    @GetMapping("/")

    public String hello() {

        return "Hello, World!";

    }

}

```

Ensure you have the `spring-boot-starter-web` dependency in your project's build file.

### 2. Dockerizing for Containerization

```dockerfile

FROM openjdk:17-jdk-alpine

WORKDIR /app

COPY target/*.jar app.jar

EXPOSE 8080

ENTRYPOINT ["java", "-jar", "/app/app.jar"]

```

Build and run locally:

```bash

docker build -t your-dockerhub-username/hello-world-app:latest .

docker run -d -p 8080:8080 your-dockerhub-username/hello-world-app:latest

```

### 3. Automating with GitHub Actions (Including Secrets Setup)

Now, let's set up the automation using GitHub Actions, focusing on how to add the necessary secrets.

#### 3.1. Setting up Secrets in GitHub (Step-by-Step UI)

Here's how to add your Docker Hub credentials as secrets in your GitHub repository:

1.  Navigate to your Repository: Go to the main page of your GitHub repository.

2.  Click on "Settings": You'll find this tab towards the right of the menu bar (next to "Insights").

3.  Go to "Secrets and variables" then "Actions": In the left sidebar, scroll down until you see "Secrets and variables". Click on it, and then click on "Actions".

4.  Click "New repository secret": On the "Actions secrets" page, you'll see a button labeled "New repository secret". Click on it.

5.  Add the `DOCKERHUB_USERNAME` secret:

    * In the "Name" field, type: `DOCKERHUB_USERNAME`

    * In the "Value" field, enter your Docker Hub username.

    * Click the "Add secret" button.

6.  Add the `DOCKERHUB_TOKEN` secret:

    * Click the "New repository secret" button again.

    * In the "Name" field, type: `DOCKERHUB_TOKEN`

    * In the "Value" field, enter your Docker Hub personal access token (generate one from your Docker Hub settings).

    * Click the "Add secret" button.

You should now see `DOCKERHUB_USERNAME` and `DOCKERHUB_TOKEN` listed under your repository secrets.

#### 3.2. Creating the GitHub Actions Workflow

Create `.github/workflows/ci-cd.yml`:

```yaml

name: CI/CD Pipeline

on:

  push:

    branches:

      - main

jobs:

  build-and-push:

    runs-on: ubuntu-latest

    steps:

      - name: Checkout code

        uses: actions/checkout@v4

      - name: Set up JDK

        uses: actions/setup-java@v4

        with:

          java-version: '17'

          distribution: 'temurin'

      - name: Build with Maven

        run: ./mvnw clean package -DskipTests

      - name: Login to Docker Hub

        uses: docker/login-action@v3

        with:

          username: ${{ secrets.DOCKERHUB_USERNAME }}

          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Build and push Docker image

        run: |

          docker build -t ${{ secrets.DOCKERHUB_USERNAME }}/hello-world-app:${{ github.sha }} .

          docker push ${{ secrets.DOCKERHUB_USERNAME }}/hello-world-app:${{ github.sha }}

          docker tag ${{ secrets.DOCKERHUB_USERNAME }}/hello-world-app:${{ github.sha }} ${{ secrets.DOCKERHUB_USERNAME }}/hello-world-app:latest

          docker push ${{ secrets.DOCKERHUB_USERNAME }}/hello-world-app:latest

```

### 4. Ready for Kubernetes: Deployment Manifest

```yaml

apiVersion: apps/v1

kind: Deployment

metadata:

  name: hello-world-app

spec:

  replicas: 2

  selector:

    matchLabels:

      app: hello-world-app

  template:

    metadata:

      labels:

        app: hello-world-app

    spec:

      containers:

        - name: hello-world-container

          image: your-dockerhub-username/hello-world-app:latest

          ports:

            - containerPort: 8080

```

### 5. Ready for Kubernetes: Service Manifest

```yaml

apiVersion: v1

kind: Service

metadata:

  name: hello-world-service

spec:

  selector:

    app: hello-world-app

  ports:

    - protocol: TCP

      port: 80

      targetPort: 8080

  type: LoadBalancer

```

### Deploying to Kubernetes

```bash

kubectl apply -f deployment.yaml

kubectl apply -f service.yaml

```

```bash

kubectl get deployments

kubectl get services

```

---