Running your Spring Boot App with Docker

In this article, we will learn:

• What is Docker

• Why use Docker

• How to use Docker to run a Spring Boot application (we will keep it short and sweet)

What is Docker?

Docker is a tool that allows us to run and distribute our applications in isolated environments called containers.

A Docker container is a lightweight, portable, and isolated environment where an application runs. It includes:

✅ The application code
✅ All its dependencies (libraries, runtime, etc.)
✅ A minimal OS environment (without the full OS)

This ensures the application runs exactly the same way across different machines, whether it’s your laptop, a server, or the cloud. 🚀

Why use Docker?

Without Docker, developers often face:

• ❌ "It works on my machine!" but fails in production.

• ❌ Dependency hell—conflicting OS versions, libraries, and configurations.

• ❌ Slow and bloated VMs that take up too many resources.

✅ Docker solves this by packaging everything into a lightweight, portable container, so your app runs the same way everywhere—from your laptop to production.

With that in mind, let’s go ahead and use it to deploy a simple Spring Boot App that runs on port 8080.

♦︎ Prerequisites:

You need a Spring Boot application that runs on port 8080. I have done this recently, see my article if you need guidance.

📌 Setting Up & Running your App in Docker

1️⃣ Install Docker

1. Download and install Docker Desktop from Docker’s official website.

2. Verify the installation by running:

    docker --version
   

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2️⃣ Create a Dockerfile for Your App

1. Inside the project root directory, create a new file named Dockerfile (no extension).

2. Write the following content inside Dockerfile:

    # Use an official Java 21 runtime as the base image
    FROM eclipse-temurin:21-jdk-alpine
   
    # Set the working directory inside the container
    WORKDIR /app
   
    # Copy the built JAR file into the container
    COPY target/blog-posts-app.jar app.jar
   
    # Expose the application port
    EXPOSE 8080
   
    # Run the application
    CMD ["java", "-jar", "app.jar"]
   

   👉 "Make sure to update blog-posts-app.jar with your actual JAR filename and verify that the Java version in the Dockerfile matches your project requirements."

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3️⃣ Modify pom.xml to Control JAR Filename

1. Open pom.xml in the project directory.

2. Inside the <build> section, add the following to ensure the generated JAR file has a consistent name (the same name that you have used on your docker file):

    <finalName>blog-posts-app</finalName>
   

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4️⃣ Build the Docker Image

1. Package the Spring Boot application into a JAR file:

    # Package the Spring Boot app
    mvn clean package
   

2. Build the Docker image:

    # Build the Docker image
    docker build -t blog-posts-app .
   

   (Remember to use the name of your app)

   🚀 Tip: A Docker image is the final, packaged version of an application, created using a Dockerfile.
   It’s like a pre-installed application that you can run anywhere.

---

5️⃣ Run the Container

1. Start the container from the built image:

    # Run the docker container
    docker run -d -p 8080:8080 --name blog-posts-app blog-posts-app
   

   (Replace in this command the name of your app and image name)

2. Verify that the container is running:

    ## List the running containers
    docker ps
   

3. Test the application by running it on your browser:

   For example, in my case is: http://localhost:8080/api/posts

   

🎯 What We Achieved Today:

• 📦 Packaged our Spring Boot app with Maven.

• 📜 Created a Dockerfile to containerize the app.

• 🖼️ Built a Docker image from the Dockerfile.

• 🚀 Deployed the app inside a Docker container.

• 🔥 Successfully tested it in a browser.

Now, your Spring Boot app runs in a portable, isolated environment.
✅ Next step? You can add a database, use Docker Compose, or deploy it to the cloud!

📌 Explore More

Want to see this in action? **Check out my project on GitHub:**🔗 GitHub Repo