I recently started reading about the “Containerization” of applications using docker.

In order to try it out for me we are going to cover here some docker commands, starting from the build, pull/push, run, delete, load, etc…

Prerequisites

I have created a very simple Springboot application which is packaged in a jar.

I have also created a free account in DockerHub (https://hub.docker.com/) as my docker registry.

I also assumed you have the below basics:

  • ✔ Maven (or use a Maven Wrapper)
  • ✔ Docker

Let’s get into business!

1) Package your application using maven

mvn clean install package

This will create a jar under your ‘/target’ project directory

Test your packaged application if to make sure it starts well

  • Run my demo jar 
    java -jar /target/demo-0.0.1-SNAPSHOT.jar
  • Check if it started using the ‘curl’ command 
    curl localhost:8080

2) Create your Dockerfile

A dockerfile is a text document containing all the commands needed to create your container image.

Use ‘touch’ command to create a blank file

touch Dockerfile

Add the below commands in your Dockerfile:

FROM openjdk:8-alpine
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

The above commands instructs:

  • To use the open jdk8 alpine as a base image
  • Use ARG command to set the jar file name
  • Copy the jar and rename to app.jar
  • Set the entry point to start your application

3) Now we’re ready to build the image!

We will build our image with the name ‘helloworld-docker-app’ from our project root directory

docker build -t helloworld-docker-app .

To see the images you’ve created:

docker images

4) Push the image to docker registry

Prerequisite:

  • Login to docker registry by 
    docker login
  • (For free dockerhub account) Tag the image with your docker user id. Note: You can use ‘tag’ or ‘-t’ 
    docker tag [image name] [new image name]
docker tag helloworld-docker-app maiajosipin/helloworld-docker-app

Push!

docker push maiajosipin/helloworld-docker-app

Here’s the uploaded image from dockerhub.

5) Let’s try to run our image

Since we already have our image in our local workspace, we will not pull from docker registry, but you can do so by executing

docker pull maiajosipin/helloworld-docker-app

To run our app, set the port to 8080:

docker run helloworld-docker-app -p 8080:8080

Test using ‘curl’ command we also used earlier:

curl localhost:8080

And we’re done! 🙂

6) Additionally, you can delete the image from your local

docker rmi [image name]
docker rmi helloworld-docker-app

Verify using:

docker images

Happy docker! ��