thorntail

Java Thorntail Maven Docker example

Clone this repository with git clone https://github.com/danial-k/docker-intro.git and open docker-intro/thorntail in an IDE.

Alternatively, to skip cloning and use these instructions directly, create a new directory for this example:

mkdir -p docker-intro/thorntail
cd docker-intro/thorntail

Setting up a development container

Create and connect to a Maven container:

docker run \
-it \
--name thorntail \
--hostname thorntail \
--mount type=bind,src=`pwd`/app,dst=/app \
--publish 3015:8080/tcp \
-w //app \
maven:3.6-jdk-8 \
bash

If you've cloned this project and just want to see the build process, you may skip to Run the application with the Maven thorntail plugin. Otherwise, create a pom.xml file in the app directory, with the same content as the pom.xml from this repository.

Create the source directory:

mkdir -p src/main/java/com/example/thorntail

In this directory create RestApplication.java, defining /rest as the root API path, with the following content:

package com.example.thorntail;

import javax.ws.rs.core.Application;
import javax.ws.rs.ApplicationPath;

@ApplicationPath("/rest")
public class RestApplication extends Application {
}

Then create HelloWorldEndpoint.java with the following content, defining the /rest/hello endpoint

package com.example.thorntail;

import javax.ws.rs.Path;
import javax.ws.rs.core.Response;
import javax.ws.rs.GET;
import javax.ws.rs.Produces;

@Path("/hello")
public class HelloWorldEndpoint {

  @GET
  @Produces("text/plain")
  public Response doGet() {
    return Response.ok("Hello World!").build();
  }
}

Run the application with the Maven thorntail plugin:

mvn package
mvn thorntail:run

The running application should be visible at http://127.0.0.1:3015/rest/hello. Although the application is functioning, it is not production optimised because of the base Maven image it is running on. For release, the application will be packaged as an uberjar (all dependecies bundled) and run as a regular java -jar process on a JRE base image.

Building deployment container

To publish the application as a self-contained image, we will use a multi-stage build process (see the Dockerfile for this project. This Dockerfile will first build the source (using on the Maven image) and then produce a deployable image (based on the OpenJDK JRE image):

docker build -t thorntail:1.0.0 .

This will send all files in the current directory to the Docker daemon's build context (excluding paths specified in .dockerignore), then create and tag the image. With the exclusions specified, the build context is approximately 15KB, without which, it is approximately 80MB. Once the image has been built, run with:

docker run -p 3016:8080 thorntail:1.0.0

The application should now be visible at http://127.0.0.1:3016/rest/hello.