Dockly: Building Ready-to-Launch Docker Images

We needed a way to take a git repo and make it ready to launch. We wanted to take the repo, add it to a Docker image, build assets, generate startup scripts, and package it in a Debian package for easy deployment - all in under 20 lines of code.

So we built Dockly to provide a simple syntax to define exactly how our deployment packages are built.

From repo to container

Describe putting your app into a Docker container with:

docker :my_image do
  import 's3://.../base-image.tar.gz'
  git_archive '/app'

  build <<-EOF
    run cd /app && ./configure && make
  EOF
end

• The import command specifies the base image.
• The git_archive command puts the git archive of your app into the /app path, or wherever you want to put it.
• The build command allows you to run commands from the context of the Docker container. Anything that is valid in a Dockerfile can go here.

Adding init scripts

Generate your init scripts to control the Docker processes using foreman:

foreman :my_app do
  log_dir '/data/logs'
  user 'appuser'
end

You can customize the init scripts with all the same options as foreman export.

Pulling it all together

Pull the docker and foreman definitions into a Debian package:

deb :my_package do
  package_name 'my_app'
  docker :my_image
  foreman :my_app
end

Or, if you prefer nesting, you can inline your definitions. All together this looks like:

deb :my_package do
  package_name 'my_app'

  docker do
      name 'my_image'
      import 's3://.../base-image.tar.gz'
      git_archive '/app'

      build <<-EOF
        run cd /app && ./configure && make
      EOF
  end

  foreman do
    name 'my_app'
    log_dir '/data/logs'
    user 'appuser'
  end
end

Your Turn!

There's a lot more Dockly can do to package your applications. Features include build caching, mixing in files and directories and including pre/post install/uninstall scripts. When built, we push the final image to S3.

We're packaging more than just Rails applications: we use Dockly to nicely wrap up Node projects and other services.

Dockly is open source. Try it out!