Rails Engine Skeleton

my_engine/
  app/
    controllers/my_engine/application_controller.rb
    models/my_engine/
    services/my_engine/
  config/
    routes.rb
  lib/
    my_engine.rb
    my_engine/version.rb
    my_engine/configuration.rb
    my_engine/engine.rb
  spec/
    dummy/
    lib/
    requests/
    services/
  my_engine.gemspec

require "my_engine/version"
require "my_engine/configuration"
require "my_engine/engine"

module MyEngine
  class << self
    attr_writer :configuration

    def configuration
      @configuration ||= Configuration.new
    end

    def configure
      yield(configuration)
    end
  end
end

module MyEngine
  class Configuration
    attr_accessor :user_class, :audit_events

    def initialize
      @user_class = "User"
      @audit_events = false
    end
  end
end

module MyEngine
  class Engine < ::Rails::Engine
    isolate_namespace MyEngine

    initializer "my_engine.configuration" do
      config.my_engine = MyEngine.configuration
    end

    config.to_prepare do
      # Reload-safe host integration only.
    end
  end
end

MyEngine::Engine.routes.draw do
  root to: "home#index"
end

module MyEngine
  class ApplicationController < ActionController::Base
  end
end