Rails Integration

This guide explains how to host Rails applications with Falcon.

Integration with Rails

Because rails apps are built on top of rack, they are compatible with falcon.

  1. Add gem 'falcon' to your Gemfile and perhaps remove gem 'puma' once you are satisfied with the change.
  2. Run falcon serve to start a local development server.

Thread Safety

With older versions of Rails, the Rack::Lock middleware can be inserted into your app by Rails. Rack::Lock will cause both poor performance and deadlocks due to the highly concurrent nature of falcon. Other web frameworks are generally unaffected.

Rails 3.x (and older)

Please ensure you specify config.threadsafe! in your config/application.rb:

module MySite
	class Application < Rails::Application
		# ...
		# Enable threaded mode

Rails 4.x

Please ensure you have config.allow_concurrency = true in your configuration.

Rails 5.x+

This became the default in Rails 5 so no change is necessary unless you explicitly disabled concurrency, in which case you should remove that configuration.


Falcon supports rack.hijack and is compatible with ActionCable. If you use the async adapter, you should run Falcon in threaded mode, or in forked mode with --count 1. Otherwise, your messaging system will be distributed over several processes with no IPC mechanism. You might like to try out async-redis as an asynchronous message bus.