Containerizing Java applications | Creating a Spring Boot App using Dockerfile

The goal of this article is to containerize a Java application easily, by creating a Spring Boot App using Dockerfile.

The steps will be as follows:-

1. Setting up a spring-boot app
2. Creating a dockerfile
3. Building project jar
4. Building docker image by using dockerfile
5. Running image

Let’s examine the above steps in detail:

1. Setting up spring-boot app: So first of all, use spring initializer to have a very basic spring-boot greetings project with the help of a web dependency.

   

   The project includes a simple rest controller with a simple greeting message.

   

   To run this app use command:

   mvn spring-boot:run

2. Creating A Dockerfile: A dockerfile is a text document which contains commands read by docker and is executed in order to build a container image.

   

   • FROM: The keyword FROM tells Docker to use a given base image as a build base. In this case Java8 is used as base image with jdk-alpine as tag. A tag can be thought as a version.
   • COPY: copying .jar file to the build image inside /usr/app.
   • WORKDIR: The WORKDIR instruction sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow in the Dockerfile. Here the workdir is switched to /usr/app
   • RUN: The RUN instruction runs any command mentioned.
   • ENTRYPOINT: Tells Docker how to run application. Making array to run spring-boot app as java -jar .jar.
3. Building Project Jar: Now run mvn install to build a .jar file in target directory.
4. Building Docker Image: Execute command docker build -t spring-boot-docker-demo .

   

5. Run the image build: Execute command docker run spring-boot-docker-demo

   

Github repository: Spring Boot Docker Demo