Hi!

I was following your article on this topic and found out that when you run

ConnectBy.configure do |config|
  config.application_controller = "ApplicationController"
end

the object you yield is actually a subclass of Rails::Engine, not an instance of it. This means that if you have multiple initializers that configure multiple engines they're all going to overwrite whatever the previous initializer configured.

You can give it a try by adding another engine (let's say... ChatBy) and trying to setup a different application_controller for it. You'll find that now ConnectBy will have the application_controller you set for ChatBy.