Deploying Java on Kubernetes: A Basic Guide for Beginners

Deploying Java on Kubernetes: A Basic Guide for Beginners

Modern Java development is unthinkable without containerization and orchestration. Kubernetes (K8s) has become the de facto standard for managing containerized applications. In this guide, we will walk through the process of deploying a simple Java application to a Kubernetes cluster step by step. You will learn how to package your code into a Docker image, create the necessary manifests, and run the application in a production-like environment.

1. Preparing the Java Application and Docker Image

Let's start with a simple Spring Boot application. Create a Dockerfile in the root directory of your project:

FROM openjdk:17-jdk-alpine\nWORKDIR /app\nCOPY target/my-app.jar app.jar\nEXPOSE 8080\nENTRYPOINT ["java", "-jar", "app.jar"]

Build the image and push it to a registry (e.g., Docker Hub):

mvn clean package -DskipTests\ndocker build -t myregistry/my-java-app:v1 .\ndocker push myregistry/my-java-app:v1

Make sure the image works locally:

docker run -p 8080:8080 myregistry/my-java-app:v1

2. Basic Kubernetes Objects

To deploy a Java application, we need three key resources:

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• Deployment — manages replicas and updates
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• Service — provides network access to pods
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• Ingress — (optional) external traffic routing
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Creating a Deployment (deployment.yaml)

apiVersion: apps/v1\nkind: Deployment\nmetadata:\n  name: java-app-deployment\nspec:\n  replicas: 3\n  selector:\n    matchLabels:\n      app: java-app\n  template:\n    metadata:\n      labels:\n        app: java-app\n    spec:\n      containers:\n      - name: java-app\n        image: myregistry/my-java-app:v1\n        ports:\n        - containerPort: 8080\n        resources:\n          requests:\n            memory: "256Mi"\n            cpu: "250m"\n          limits:\n            memory: "512Mi"\n            cpu: "500m"\n        livenessProbe:\n          httpGet:\n            path: /actuator/health\n            port: 8080\n          initialDelaySeconds: 30\n          periodSeconds: 10\n        readinessProbe:\n          httpGet:\n            path: /actuator/health\n            port: 8080\n          initialDelaySeconds: 20\n          periodSeconds: 5

Creating a Service (service.yaml)

apiVersion: v1\nkind: Service\nmetadata:\n  name: java-app-service\nspec:\n  selector:\n    app: java-app\n  ports:\n  - protocol: TCP\n    port: 80\n    targetPort: 8080\n  type: ClusterIP

3. Deploying to a Kubernetes Cluster

Apply the manifests to your cluster (make sure kubectl is configured):

kubectl apply -f deployment.yaml\nkubectl apply -f service.yaml

Check the status of pods and the service:

kubectl get pods\nkubectl get svc java-app-service

For external access (e.g., for testing), use port-forward:

kubectl port-forward service/java-app-service 8080:80

Now the application is available at http://localhost:8080.

4. Scaling and Updating

Kubernetes makes it easy to scale the application:

kubectl scale deployment java-app-deployment --replicas=5

To update the image (rolling update), change the tag in the Deployment and apply:

kubectl set image deployment/java-app-deployment java-app=myregistry/my-java-app:v2\nkubectl rollout status deployment/java-app-deployment

If necessary, roll back the changes:

kubectl rollout undo deployment/java-app-deployment

Conclusion

We have covered the basic process of deploying a Java application on Kubernetes.