Now that we have a running Gogs installation for our source code (see here) - we can use Drone to build working software from those repos. Drone is an Continious Integration System, that comes in two flavors: Drone.io - which is the hosted service you could use - or Drone - as self-hosted service. We want to use the later one. To install drone in our existing Docker setup (with gogs already installed) we need to complete following steps:

# Create docker-compose.yml in ~/drone/
cd ~
mkdir drone
cd drone
vi docker-compose.yml
# Copy this content into your docker-compose.yml file

drone:
  restart: unless-stopped
  image: drone/drone:0.4.2
  volumes:
    - /var/drone:/var/lib/drone
    - /var/run/docker.sock:/var/run/docker.sock
  env_file:
    - ./dronerc
  ports:
    - "8000:8000"

# Create the dronerc file
vi dronerc
# Copy this content into your dronerc file
# replace yourserverip with the ip or dns name of your server, i.e. example.com
# replace the gogsport with the port of the http port of the gogs installation, i.e. was 3000 in our example

REMOTE_DRIVER=gogs
REMOTE_CONFIG=https://yourserverip:gogsport?open=false
DEBUG=true

# Create the needed folders
sudo mkdir /var/drone
sudo chown -R yourusername:yourusername /var/drone/

After that, an docker-compose up will start the service, you can end it via STRG + C and really start it in deattached mode with docker-compose up -d
You can then go to http://yourserverip:8000 and log in into drone with your gogs login and allow access.

The current readme for drone can be found on http://readme.drone.io/usage/overview/ and you'll need to include a .drone.yml in your repos to really build something.

In my example, I used this .drone.yml

cache:
  mount:
    - /drone/.m2

build:
  main:
    image: maven:3-jdk-8-onbuild
    commands:
      - mvn clean install -Pcoverage -Dmaven.repo.local=/drone/.m2
      - mvn package -Dmaven.repo.local=/drone/.m2
      - mvn test -Dmaven.repo.local=/drone/.m2
      - echo "Build has been completed."

debug: true

and this pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.mycompany.app</groupId> 
  <artifactId>WhereIsMyPi</artifactId>
  <version>1.0</version>
  <packaging>jar</packaging>
 
  <name>Where is my Pi</name>
  <url>http://www.nico-maas.de</url>

  <build>
    <sourceDirectory>src</sourceDirectory>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.5</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
      <plugin>
       <!-- Build an executable JAR -->
       <groupId>org.apache.maven.plugins</groupId>
       <artifactId>maven-jar-plugin</artifactId>
       <version>2.4</version>
       <configuration>
        <archive>
          <manifest>
            <addClasspath>true</addClasspath>
            <classpathPrefix>lib/</classpathPrefix>
            <mainClass>WMP</mainClass>
          </manifest>
        </archive>
       </configuration>
      </plugin>
    </plugins>
  </build> 

</project>

to build my "WhereIsMyPi" project :).
Happy building!