I have a gem which is mounted as engine in my rails app via

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Editorial Team

Asked: June 15, 20262026-06-15T23:20:08+00:00 2026-06-15T23:20:08+00:00

I have a gem which is mounted as engine in my rails app via

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I have a gem which is mounted as engine in my rails app via routes.rb & Gemfile. Here are the important pieces:

Apps’ Gemfile

source 'https://rubygems.org'

gem 'rails', '3.2.9'
gem 'mysql2'


group :assets do
  gem 'sass-rails'
  gem 'coffee-rails'
end
gem 'jquery-rails'
gem "common_client", path: "../common-client"

App’s routes.rb

mount CommonClient::Engine => "", :as => 'shared'

gem’s routes.rb

get '/register' => 'session#new_registration'

gems’s SessionController

require 'common_client/session_controller_base'

class SessionController < ApplicationController

  include CommonClient::SessionControllerBase
end

gems’s SessionControllerBase

module CommonClient

  module SessionControllerBase

  def new_registration
      #some code goes here
  end
end

This works just fine in development & rails is able to find CommonClient::SessionController & execute new_registration action whenever visitor hits /register route. But in Production, rails is unable to find CommonClient::SessionController & generates the following error:

$ RAILS_ENV=production rails s
=> Booting WEBrick
=> Rails 3.2.9 application starting in production on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2012-12-09 03:27:29] INFO  WEBrick 1.3.1
[2012-12-09 03:27:29] INFO  ruby 1.9.3 (2012-10-12) [x86_64-linux]
[2012-12-09 03:27:29] INFO  WEBrick::HTTPServer#start: pid=4248 port=3000
Started GET "/" for 127.0.0.1 at 2012-12-09 03:28:17 +0530
Processing by WelcomeController#index as HTML
Redirected to localhost:3000/register
Filter chain halted as :check_credentials rendered or redirected
Completed 302 Found in 267ms (ActiveRecord: 0.0ms)
Started GET "/register" for 127.0.0.1 at 2012-12-09 03:28:18 +0530

ActionController::RoutingError (uninitialized constant CommonClient::SessionController):
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/inflector/methods.rb:230:in `block in constantize'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/inflector/methods.rb:229:in `each'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/inflector/methods.rb:229:in `constantize'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/routing/route_set.rb:69:in `controller_reference'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/routing/route_set.rb:54:in `controller'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/routing/route_set.rb:32:in `call'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:68:in `block in call'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `each'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/routing/route_set.rb:601:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/engine.rb:479:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/railtie/configurable.rb:30:in `method_missing'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:68:in `block in call'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `each'
  vendor/bundles/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/routing/route_set.rb:601:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/etag.rb:23:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/conditionalget.rb:25:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/head.rb:14:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/params_parser.rb:21:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/flash.rb:242:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/session/abstract/id.rb:205:in `context'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/session/abstract/id.rb:200:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/cookies.rb:341:in `call'
  vendor/bundles/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/query_cache.rb:64:in `call'
  vendor/bundles/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/callbacks.rb:405:in `_run__4296103602150594596__call__1936882885794917979__callbacks'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/callbacks.rb:405:in `__run_callback'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/callbacks.rb:81:in `run_callbacks'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/rack/logger.rb:32:in `call_app'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/rack/logger.rb:16:in `block in call'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/tagged_logging.rb:22:in `tagged'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/rack/logger.rb:16:in `call'
  vendor/bundles/ruby/1.9.1/gems/actionpack-3.2.9/lib/action_dispatch/middleware/request_id.rb:22:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/methodoverride.rb:21:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/runtime.rb:17:in `call'
  vendor/bundles/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/lock.rb:15:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-cache-1.2/lib/rack/cache/context.rb:136:in `forward'
  vendor/bundles/ruby/1.9.1/gems/rack-cache-1.2/lib/rack/cache/context.rb:245:in `fetch'
  vendor/bundles/ruby/1.9.1/gems/rack-cache-1.2/lib/rack/cache/context.rb:185:in `lookup'
  vendor/bundles/ruby/1.9.1/gems/rack-cache-1.2/lib/rack/cache/context.rb:66:in `call!'
  vendor/bundles/ruby/1.9.1/gems/rack-cache-1.2/lib/rack/cache/context.rb:51:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/engine.rb:479:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/application.rb:223:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/content_length.rb:14:in `call'
  vendor/bundles/ruby/1.9.1/gems/railties-3.2.9/lib/rails/rack/log_tailer.rb:17:in `call'
  vendor/bundles/ruby/1.9.1/gems/rack-1.4.1/lib/rack/handler/webrick.rb:59:in `service'
  /home/gaurish/.rvm/rubies/ruby-1.9.3-p286-perf/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  /home/gaurish/.rvm/rubies/ruby-1.9.3-p286-perf/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  /home/gaurish/.rvm/rubies/ruby-1.9.3-p286-perf/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'


^C[2012-12-09 03:42:57] INFO  going to shutdown ...
[2012-12-09 03:42:57] INFO  WEBrick::HTTPServer#start done.
Exiting

Now,
here is the interesting part. These errors goes away in production & app works just fine when I disable code caching in production.rb. by setting

config.cache_classes = false

All this makes me wonder,

why rails can CommonClient::SessionController in development env but not in production env?
How does setting config.cache_classes = false makes it work in production? And rails can find CommonClient::SessionController which it was not able to do earlier
What I need to do when so that rails finds CommonClient::SessionController other than ugly hack of disabling code cache & reloading all code on each request?

Lastly, I have tried to explain as best I could but still something is not clear or more information is required. Please leave a comment. Thanks

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1 Answer

Editorial Team · Answer 1 · 2026-06-15T23:20:09+00:00

Editorial Team

2026-06-15T23:20:09+00:00Added an answer on June 15, 2026 at 11:20 pm

Try update routes.rb like:

require 'common_client'
mount CommonClient::Engine => '/shared'

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