Introduction

In this tutorial, we’ll create a simple Hello World application and deploy in Kubernetes cluster. In localhost, we are using Docker Desktop and have enabled Kubernetes. This is a single node cluster.

Creating the application

Create a Spring Boot application. Following is the pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.4.3</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.learnitweb</groupId>
	<artifactId>helloworld</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>helloworld</name>
	<description>Demo project for Spring Boot</description>
	<url/>
	<licenses>
		<license/>
	</licenses>
	<developers>
		<developer/>
	</developers>
	<scm>
		<connection/>
		<developerConnection/>
		<tag/>
		<url/>
	</scm>
	<properties>
		<java.version>17</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<finalName>helloworld</finalName>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Create the HelloWorldController:

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

@RestController
@RequestMapping("/api")
public class HelloWorldController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

Create the Docker file

In the root folder of your application, create a Dockerfile:

FROM openjdk:17-jdk-slim
WORKDIR /app
COPY target/*.jar helloworld.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "helloworld.jar"]

Now build the image:

docker build -t hello-world-app .

Since you’re using a single-node cluster (Docker Desktop), you don’t need to push the image to Docker Hub. Instead, you can use the locally built image.

Create a Kubernetes Deployment

Create a new file named deployment.yaml in your project root:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
        - name: hello-world
          image: hello-world-app  # Using locally built image
          imagePullPolicy: Never  # Prevents Kubernetes from pulling from Docker Hub
          ports:
            - containerPort: 8080

---
apiVersion: v1
kind: Service
metadata:
  name: hello-world-service
spec:
  selector:
    app: hello-world
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
  type: LoadBalancer  # Exposes service externally (on Docker Desktop, use port-forward)

Apply the Deployment

Run the following commands to deploy:

kubectl apply -f deployment.yaml

>kubectl apply -f deployment.yml
deployment.apps/hello-world-deployment created
service/hello-world-service created

Since Docker Desktop Kubernetes doesn’t assign an external IP, use:

kubectl port-forward svc/hello-world-service 8080:80

>kubectl get pods
NAME                                      READY   STATUS    RESTARTS   AGE
hello-world-deployment-857c5cfcf8-cdtjp   1/1     Running   0          35m

Access the application

Now access the application:

http://localhost:8080/api/hello