How to Scale a Spring Boot Application

Welcome to the Spring Boot “Nginx” project! This is a simple project that demonstrates the way of scaling a Spring Boot Application using Nginx as a Load Balancer.

1. Overview

This project serves as a starting point for understanding how to scale a basic Spring Boot application using Docker for Containerization and Nginx for Load Balancing. It includes the necessary setup and dependencies to quickly get you up and running.

2. Prerequisites

Before you begin, ensure you have met the following requirements:

• Java Development Kit (JDK) installed (version 17 or higher)
• Maven build tool installed
• Nginx, Docker installed**

3. Maven Dependencies

First, we need to add the dependencies to our pom.xml.

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

4. The Controller

@RestController
public class HelloController {

    @GetMapping("/")
    public String helloWorld() {
        return "Hello World";
    }

    @GetMapping("/check")
    public String check() {
        try {
            return "Container ID: " + InetAddress.getLocalHost().getHostName();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
        return "checking failed";
    }
}

5. Dockerizing the Project

5.1. Dockerfile

FROM eclipse-temurin:17-alpine
RUN mkdir /opt/app
COPY target/*.war /opt/app/app.war
ENTRYPOINT ["java", "-jar", "/opt/app/app.war"]

5.2. Build the WAR file

mvn clean package

5.3. Build the Docker image

docker build -t nginx .

Go to the project directory and run these above commands

5.4. Run the Docker container

docker run -d -p 1111:8080 nginx:latest
docker run -d -p 2222:8080 nginx:latest
docker run -d -p 3333:8080 nginx:latest

Run 3 containers with the Docker image

6. Editing Nginx Config

http {
	include mime.types;

	upstream backendserver {
		server localhost:1111;
		server localhost:2222;
		server localhost:3333;
	}

	server {
		listen 8080;

		location / {
			proxy_pass http://backendserver/;
		}
	}
}

events {}

Go to /etc/nginx & edit nginx.conf file with the above config & restart nginx

7. Check if Nginx Load Balancer is Working

curl http://localhost:8080/check

Check if the response contains different container identifiers.

By combining these steps, you should be able to determine whether Nginx is successfully round-robin distributing requests among your Spring Boot containers.

Here is the Github Repo for this Article!