Containerizing Java applications | Creating a Spring Boot App using Dockerfile
The steps will be as follows:-
- Setting up a spring-boot app
- Creating a dockerfile
- Building project jar
- Building docker image by using dockerfile
- Running image
Let’s examine the above steps in detail:
- 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:
- 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.
- Building Project Jar: Now run mvn install to build a .jar file in target directory.
- Building Docker Image: Execute command docker build -t spring-boot-docker-demo .
- Run the image build: Execute command docker run spring-boot-docker-demo
Github repository: Spring Boot Docker Demo