Motorhead is a prototyping framework for Rails. It's something akin to "feature toggle". It can be used for "A/B testing" as well. But essentially, the main purpose of this framework is to provide a way to rapidly and safely deliver new features to the production environment.

Bundle into your Rails app.

Motorhead helps you mounting specially creafted Isolated Engines onto the main Rails app. An engine can contain whole MVC components, which means that you can encapsulate everything that are needed for your new feature under one single directory. This helps your team creating multiple new features simultaneously without causing code conflict.

Each Motorhead engine can be configured to be enabled/disabled. The condition is not just a flag but can be a Ruby Proc which will be dynamically evaluated on each request in the controller context.

If any RuntimeError happens inside an engine on the production environment, Motorhead absorbs the error and executes the appropriate fallback code so that the end users would never even notice the occurrence of the error.

Motorhead provides an interface to override the main app's controller actions.

Motorhead provides a hook to partially overwrite any part of your existing view.

main_app
├── Gemfile
├── Gemfile.lock
├── Rakefile
├── app
│   ├── assets
│   ├── controllers
│   ├── engines
│   │   ├── my_awesome_new_feature
│   │   │   ├── app
│   │   │   │   ├── assets
│   │   │   │   ├── controllers
│   │   │   │   │   └── my_awesome_new_feature
│   │   │   │   │       └── welcome_controller.rb
│   │   │   │   ├── helpers
│   │   │   │   │   └── my_awesome_new_feature
│   │   │   │   │       └── welcome_helper.rb
│   │   │   │   ├── mailers
│   │   │   │   ├── models
│   │   │   │   └── views
│   │   │   │       ├── layouts
│   │   │   │       │   └── my_awesome_new_feature
│   │   │   │       │       └── application.html.erb
│   │   │   │       └── my_awesome_new_feature
│   │   │   │           └── welcome
│   │   │   ├── config
│   │   │   │   └── routes.rb
│   │   │   ├── lib
│   │   │   │   ├── my_awesome_new_feature
│   │   │   │   │   └── engine.rb
│   │   │   │   ├── my_awesome_new_feature.rb
│   │   │   │   └── tasks
│   │   │   ├── my_awesome_new_feature.gemspec
│   │   │   └── test
│   │   └── yet_another_new_feature
│   │       ├── app
│   │       ...
│   ├── helpers
│   ├── mailers
│   ├── models
│   └── views
├── bin
├── config
├── db
...

Put active_if directive inside the Engine class. The whole engine will only be executed if the block is evaluated to be truthy on runtime.

Example:

# app/engines/my_awesome_new_feature/config/routes.rb
module MyAwesomeNewFeature
  class Engine < ::Rails::Engine
    include Motorhead::Engine

    # this whole engine will be executed only when logged in as admin users
    active_if { current_user.admin? }
  end
end

You can configure a path to mount the Engine via mount_at directive. This value is defaulted to "/", which means the Engine routes will be mixed into the main app's routes.

Example:

# app/engines/my_awesome_new_feature/config/routes.rb
module MyAwesomeNewFeature
  class Engine < ::Rails::Engine
    include Motorhead::Engine

    # all routes inside this Engine will be prefixed by "/harley"
    mount_at 'harley'
  end
end

All routes in engines' routes.rb will be automatically prepended to the main app's Routes.

Controllers can be a normal Engine controller. Or, you can craft a controller class inheriting a controller that exists in the main app, and overriding some action methods. From inside the actions in engines, you can call the main app's action via super.

Example:

# app/engines/my_awesome_new_feature/app/controllers/my_awesome_new_feature/welcome_controller.rb
class MyAwesomeNewFeature::WelcomeController < ::WelcomeController
  include Motorhead::Controller

  def index
    # invoking the main app's action first
    super

    # adding some more business logic
    @notifications = Notification.for current_user
  end
end

When an engine renders the views, it looks up app/views/ENGINE_NAME/ directory first, then the main app's view directory next. This way you can overwrite views per template/partial file. Also, Motorhead adds new :engine option to render method, which enables you to explicitly inject a piece of HTML from an engine into any place of the app. render :engine takes an `ENGINE_NAME/view_path' parameter.

Example:

# app/engines/my_awesome_new_feature/app/views/my_awesome_new_feature/welcome/_index.html.haml
.new_feature
  Some contents for new feature

# app/views/welcome/index.html.haml
= render engine: 'my_awesome_new_feature/welcome/index' do
  Some contents that will be shown by default

Motorhead provides some handy code generators.

% rails g motorhead ENGINE_NAME

Example:

% rails g motorhead my_awesome_new_feature

This generates a motorhead Engine in ~/app/engines/my_awesome_new_feature/ directory.

% rails g motorhead ENGINE_NAME CONTROLLER_NAME [action action] [options]

Example:

% rails g motorhead my_awesome_new_feature welcome index

This generates a motorhead Engine in ~/app/engines/my_awesome_new_feature/ directory. Plus, a controller that extends WelcomeController and implements index action inside the Engine.

Motorhead includes a tiny admin console Engine call "RoadCrew" through which you can easily enable/disable each mounted Engine. To use this, require 'motorhead/road_crew' when bundling motorhead gem in your Gemfile:

# Gemfile
gem 'motorhead', path: '~/src/motorhead', require: ['motorhead', 'motorhead/road_crew']

then render the road_crew/button Engine partial to put a button inside somewhere in your view (usually in the header or footer?):

# app/views/layouts/application.html.erb
<%= render engine: 'road_crew/button' %>

You might also want to configure the RoadCrew Engine's active_if directive for security.

# config/initializers/mh_road_crew.rb
RoadCrew::Engine.active_if { current_user.admin? }

Pull requests are welcome on GitHub at https://github.com/amatsuda/motorhead.

• Better generator

• Model extension

• Documentation

This product is deeply inspired by Chanko.

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