Rails Routes Constraints By Subdomain

routes.rb

constraints(lambda { |req| req.host.to_s =~ /\Aadmin./ }) do
  namespace :admin, :path => '/' do
    root :to => 'dashboards#show' # => that's Admin::DashboardsController#show in app/controllers/admin/dashboards_controller.rb
    resources :users              # => Admin::UsersController in app/controllers/admin/users_controller.rb
    resources :posts              # => Admin::PostsController in app/controllers/admin/posts_controller.rb
  end
end