-app
    -backend
        -controllers
        -models
        -helpers
        -assets
        -views
    -frontend
        -controllers
        -models
        -helpers
        -assets
        -views
    -common
        -controllers
        -models
        -helpers
        -assets
        -views

-controllers
    -frontend/
    -backend/
    -common/

config.path_to_app = case request.subdomain
                          when 'admin' then 'app/backend'
                          when 'api' then 'app/api'
                          else 'app/frontend'
                     end