Pull Dog: Automatic Docker Test Environments for Pull Requests

Today, almost every developer is using a managed Git service like GitHub. When writing code, this is almost essential, no matter if you’re alone or in a team.

But there are many ways to organize code. What I’ve seen most people do is to branch out when they make a new feature, and create a “Pull Request” when they have finished that feature.

This allows for several benefits:

1. Someone can review the code before it is merged.
2. Someone can clone the code and test it on their machine, to make sure nothing broke.

But that second step can be quite tedious and annoying, especially if the person that needs to test the feature is not a developer.

This is where Pull Dog comes in to play.

Pull Dog logo

Pull Dog is a GitHub app that will automatically provision a Docker-based test server for your feature as you open a pull request. And best of all — it’s all free!

Setting it up

You start out by installing the app to your GitHub account.

After that, you simply push a commit to the master branch of the repository you want to enable, with a pull-dog.json file in the root directory that contains the following.

{
  "dockerComposeYmlFilePaths": [
    "your/path/to/docker-compose.yml"
  ]
}

After pushing, Pull Dog is enabled for the given repository and will run for any future pull requests that are opened.

Trying it out

For my example, I made an empty repository with the following pull-dog.json configuration file:

{ "dockerComposeYmlFilePaths": ["docker-compose.yml"] }

And the following docker-compose.yml file, containing a basic WordPress and MySQL setup.

version: '3.3'
  
 services:
  db:
    image: mysql:5.7
    volumes:
    - db_data:/var/lib/mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: somewordpress
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD: wordpress
  
  wordpress:
    depends_on:
    - db
    image: wordpress:latest
    ports:
    - "8000:80"
    restart: always
    environment:
      WORDPRESS_DB_HOST: db:3306
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_PASSWORD: wordpress
      WORDPRESS_DB_NAME: wordpress
 volumes:
   db_data: {}

Opening a pull request

Upon opening my pull request, I am greeted with the following comment from pull-dog where I can see that it is provisioning a server for me.

Pull Dog is provisioning a server here after opening the pull request

After a brief while, the comment is updated with the connection details of my server (note that the port 8000 is the exposed port from the docker-compose.yml file).

The server is ready

Closing the pull request

After closing the pull request, the server is shut down again, and the comment is updated to reflect that.