app_proxy_controller.rb

class AppProxyController < ApplicationController


  def by_product
    #render layout: false, content_type: 'application/json'
    @product = Course.find_by(product_id: params[:product_id])
    respond_to do |format|
      format.json #{ render json: @product }
    end
  end

end

error.rb

vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/inflector/methods.rb:259:in `each'
2017-06-06T22:15:28.753084+00:00 app[web.1]: ActionController::RoutingError (uninitialized constant AppProxy):
2017-06-06T22:15:28.753091+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/routing/route_set.rb:60:in `controller'
2017-06-06T22:15:28.753090+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/routing/route_set.rb:70:in `controller_reference'
2017-06-06T22:15:28.753091+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/routing/route_set.rb:39:in `serve'
2017-06-06T22:15:28.753086+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/inflector/methods.rb:261:in `const_get'
2017-06-06T22:15:28.753092+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/journey/router.rb:43:in `block in serve'
2017-06-06T22:15:28.753089+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/inflector/methods.rb:259:in `constantize'
2017-06-06T22:15:28.753089+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/inflector/methods.rb:259:in `inject'
2017-06-06T22:15:28.753092+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/journey/router.rb:30:in `each'
2017-06-06T22:15:28.753096+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/omniauth-1.3.2/lib/omniauth/strategy.rb:164:in `call'
2017-06-06T22:15:28.753093+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/journey/router.rb:30:in `serve'
2017-06-06T22:15:28.753095+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/omniauth-1.3.2/lib/omniauth/strategy.rb:186:in `call!'
2017-06-06T22:15:28.753094+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/routing/route_set.rb:817:in `call'
2017-06-06T22:15:28.753097+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/etag.rb:24:in `call'
2017-06-06T22:15:28.753096+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/omniauth-1.3.2/lib/omniauth/builder.rb:63:in `call'
2017-06-06T22:15:28.753099+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/flash.rb:260:in `call'
2017-06-06T22:15:28.753097+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/conditionalget.rb:25:in `call'
2017-06-06T22:15:28.753098+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/params_parser.rb:27:in `call'
2017-06-06T22:15:28.753099+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/session/abstract/id.rb:225:in `context'
2017-06-06T22:15:28.753098+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/head.rb:13:in `call'
2017-06-06T22:15:28.753087+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/inflector/methods.rb:261:in `block in constantize'
2017-06-06T22:15:28.753101+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:653:in `call'
2017-06-06T22:15:28.753100+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/cookies.rb:560:in `call'
2017-06-06T22:15:28.753100+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/session/abstract/id.rb:220:in `call'
2017-06-06T22:15:28.753100+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.6/lib/active_record/query_cache.rb:36:in `call'
2017-06-06T22:15:28.753105+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:38:in `call_app'
2017-06-06T22:15:28.753104+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
2017-06-06T22:15:28.753103+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
2017-06-06T22:15:28.753102+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:88:in `__run_callbacks__'
2017-06-06T22:15:28.753102+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
2017-06-06T22:15:28.753103+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:81:in `run_callbacks'
2017-06-06T22:15:28.753103+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/callbacks.rb:778:in `_run_call_callbacks'
2017-06-06T22:15:28.753105+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:20:in `block in call'
2017-06-06T22:15:28.753106+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in `block in tagged'
2017-06-06T22:15:28.753106+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:26:in `tagged'
2017-06-06T22:15:28.753106+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/tagged_logging.rb:68:in `tagged'
2017-06-06T22:15:28.753107+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/railties-4.2.6/lib/rails/rack/logger.rb:20:in `call'
2017-06-06T22:15:28.753104+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
2017-06-06T22:15:28.753111+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/request_id.rb:21:in `call'
2017-06-06T22:15:28.753104+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
2017-06-06T22:15:28.753112+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.6/lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
2017-06-06T22:15:28.753113+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/actionpack-4.2.6/lib/action_dispatch/middleware/static.rb:120:in `call'
2017-06-06T22:15:28.753111+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/methodoverride.rb:22:in `call'
2017-06-06T22:15:28.753114+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/railties-4.2.6/lib/rails/engine.rb:518:in `call'
2017-06-06T22:15:28.753113+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/sendfile.rb:113:in `call'
2017-06-06T22:15:28.753114+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/railties-4.2.6/lib/rails/application.rb:165:in `call'
2017-06-06T22:15:28.753112+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/rack-1.6.5/lib/rack/runtime.rb:18:in `call'
2017-06-06T22:15:28.753114+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/puma-3.8.2/lib/puma/configuration.rb:224:in `call'
2017-06-06T22:15:28.753115+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/puma-3.8.2/lib/puma/server.rb:600:in `handle_request'
2017-06-06T22:15:28.753115+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/puma-3.8.2/lib/puma/server.rb:435:in `process_client'
2017-06-06T22:15:28.753116+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/puma-3.8.2/lib/puma/server.rb:299:in `block in run'
2017-06-06T22:15:28.753116+00:00 app[web.1]:   vendor/bundle/ruby/2.3.0/gems/puma-3.8.2/lib/puma/thread_pool.rb:120:in `block in spawn_thread'

rake routes.rb

...
app_proxy GET    /app_proxy/products/by_product/:product_id(.:format) app_proxy/products#by_product
     root GET
...

routes.rb

  namespace :app_proxy do
    root action: 'index'
    get 'products/by_product/:product_id', to: 'products#by_product'

  end