Docker Spring Boot tutorial. Dockerize Spring Boot app in 3 minutes.

Get Started

In this post, we will use Docker to create an image of a Spring Boot application and run it in a container.

Step 1 - Create a Spring Boot boilerplate app

Let’s create the application skeleton using the Spring Boot Initializer: http://start.spring.io, including Web as the only dependency and choosing Maven (to follow the same instructions as in this post).

Step 2 - Code a simple REST Controller

Give your Spring Boot boilerplate project downloaded, just unzip it and edit the DemoApplication.java file.

Then add a new controller to handle home using the following code:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApplication {

    @RequestMapping("/")
    public String home() {
        return "Hello World";
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Step 3 - Running the application locally

Use your local Maven installation or the wrapper (mvnw command) normally included by the Spring initializer. From the application’s root folder, execute:

$ ./mvnw spring-boot:run

This will fire up Tomcat server by default. To see your application in action, open a browser window (or use command line tools like curl or httpie) and navigate to http://localhost:8080. You should see your Hello World message:

As an alternative, you can also run the application by first packaging it in a jar file, and then run it with the java command. In that case, use Maven to create the package:

$ ./mvnw clean package

The resulting .jar file will be placed in a new target folder. Now you can execute this command and you will get the application running as before:

$ java -jar ./target/<your-file>-<version>/SNAPSHOT.jar

So far there is nothing to do with Docker, but it’s important to highlight a couple of concepts to fully understand the rest of this post:

• You used your machine to build the application (using Maven, either previously installed or the wrapper).
• You used your machine to run the application (either using the spring-boot plugin or the jar file).

Step 4 - Dockerizing Spring Boot (or any executable .jar file)

Setup Docker

Before creating a container for the Django application and shipping it off, you need to install Docker on your local machine. For learning purpose, you will install Docker Community Edition. Select your OS from the list below and follow the setup instructions:

• Mac OS
• Windows
• Ubuntu
• Debian
• CentOS
• Fedora

Make the docker App image

The next stage to improve your docker RoR workflow is adding a Dockerfile to your project. The structure of a Dockerfile can be considered a series of instructions on how to build your container/image.

Start the Dockerfile by creating an empty file named Dockerfile in the root of your project. Then, complete each instruction according to the following example:

FROM openjdk:10-jre-slim

WORKDIR /app
COPY ./target/<your-file>-<version>/SNAPSHOT.jar /app

EXPOSE 8080

CMD ["java", "-jar", "<your-file>-<version>/SNAPSHOT.jar"]

The image is based on a slim Linux with JRE 10, on top of that we change the working directory and we copy the JAR file, then we just execute the same command as we did before when running from our machine. The EXPOSE instruction is telling Docker that the 8080 port can be exposed outside the container, but note that we’ll also need to make the port available when running it anyways.

Building and Running the Container

Building the docker container is very straight forward once you have Docker and Docker Machine on your system. The following command will look for your Dockerfile and download all the necessary layers required to get your container image running. Afterwards, it will run the instructions in the Dockerfile and leave you with a container that is ready to start.

To build your Spring Boot docker container, you will use the docker build command and provide a tag or a name for the container, so you can reference it later when you want to run it. The final part of the command tells Docker which directory to build from.

$ docker build -t spring-boot-tutorial .

The final step is to run the container you have just built using Docker:

$ docker run -it -p 8080:8080 spring-boot-tutorial

The command tells Docker to run the container and forward the exposed port 8080 to port 8080 on your local machine. After you run this command, you should be able to visit http://localhost:8080 in your browser.

$ docker ps -a

To turn off your Docker container, run:

$ docker stop container_id

Push to cloud

1. Create your app

In order to install your Spring Boot project, just create a new dockerize app via cli or admin panel and set a port to 8080.

2. Push your docker container

Then just build your image and upload it to the platform.

3. Set up resources

4. Logs and app status

5. Release your app

After to click on the release button, your spring boot docker tutorial will be deployed, Just click on the generated URL and you will get your app running.

Now you can deploy your Spring Boot app without a massive build time.