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Docker::Compose

This is a Ruby OOP wrapper for the docker-compose container orchestration tool from Docker Inc.

In addition to wrapping the CLI, this gem provides an environment-variable mapping feature that allows you to export environment variables into your host that point to network services exposed by containers. This allows you to run an application on your host for quicker and easier development, but run all of its dependencies -- database, cache, adjacent services -- in containers. The dependencies can even run on another machine, e.g. a cloud instance or a container cluster, provided your development machine has TCP connectivity to every port exposed by a container.

Throughout this documentation we will refer to this gem as Docker::Compose as opposed to the docker-compose tool that this gem wraps.

Installation

Add this line to your application's Gemfile:

gem 'docker-compose'

And then execute:

$ bundle

Or install it yourself as:

$ gem install docker-compose

Usage

Invoking from Ruby code

require 'docker/compose'

# Create a new session in Dir.pwd using the file "docker-compose.yml".
# For fine-grained control over options, see Docker::Compose::Session#new
compose = Docker::Compose.new

compose.version

compose.up(detached:true)

exited = compose.ps.where { |c| !c.up? }
puts "We have some exited containers: " + exited.join(', ')

sum = compose.ps.inject(0) { |a,c| a + c.size }
puts format("Composition is using %.1f MiB disk space", sum/1024.0**2)

Invoking from Rake

Open your Rakefile and add the Docker::Compose tasks.

require 'docker/compose/rake_tasks'

Docker::Compose::RakeTasks.new do |tasks|
    # customize by calling setter methods of tasks;
    # see the class documentation for details
end

Notice that rake -T now has a few additional tasks for invoking gem functionality. You can docker:compose:env to print shell exports for host-to-container environment mapping, or you can docker:compose:host[foo].

Hosting a Command

To run a process on your host and allow it to talk to containers, use the docker:compose:host task. For example, I could enter a shell with rake docker:compose:host[bash].

Before "hosting" your command, the Rake task exports some environment variables that your command can use to discover services running in containers. Your Rakefile specifies which variables your app needs (the host_env option) and which container information each variable should map to.

By hosting commands, you benefit from easier debugging and code editing of the app you're working on, but still get to rely on containers to provide the companion services your app requires to run.

Mapping container IPs and ports

As a trivial example, let's say that your docker-compose.yml contains one service, the database that your app needs in order to run.

db:
  image: mysql:latest
  environment:
    MYSQL_DATABASE: myapp_development
    MYSQL_ROOT_PASSWORD: opensesame
  ports:
    - "3306"

Your app needs two inputs, DATABASE_HOST and DATABASE_PORT. You can specify this with the host_env option of the Rake task:

Docker::Compose::RakeTasks.new do |tasks|
    tasks.host_env = {
        'DATABASE_HOST' => 'db:[3306]',
        'DATABASE_PORT' => '[db]:3306',
    }
end

Now, I can run my services, ask Docker::Compose to map the environment values to the actual IP and port that db has been published to, and run my app:

# First, bring up the containers we will be interested in
user@machine$ docker-compose up -d

# The rake task prints bash code resembling the following:
#   export DATABASE_HOST='127.0.0.1'
#   export DATABASE_PORT='34387'
# We eval it, which makes the variables available to our shell and to all
# subprocesses.
user@machine$ eval "$(bundle exec rake docker:compose:env)"

user@machine$ bundle exec rackup

The host_env option also handles substitution of URLs, and arrays of values (which are serialized back to the environment as JSON) For example:

tasks.host_env = {
  'DATABASE_URL' => 'mysql://db:3306/myapp_development',
  'MIXED_FRUIT' => ['db:[3306]', '[db]:3306']
}

This would result in the following exports:

export DATABASE_URL='mysql://127.0.0.1:34387/myapp_development'
export MIXED_FRUIT='["127.0.0.1", "34387"]'

To learn more about mapping, read the class documentation for Docker::Compose::Mapper.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, create a GitHub release and the .gem file will be automatically uploaded to RubyGems and GitHub Packages.

The automated publication workflow renders rake release obsolete, and also makes the committed contents of version.rb irrelevant -- the version file is updated on the fly during the publish workflow. As a convention, we leave the committed file set to X.99.0-dev to signify a development copy of the gem's source code but preserve major-version compatibility. This facilitates testing of prerelease versions of this gem in other local codebases using the Gemfile path: option.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/xeger/docker-compose. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.