A Guide for Upgrading Ruby on Rails — Ruby on Rails Guides を見てみると、こんなことが書かれていて驚きました。 Autoloading is now disabled after booting in the production environment by default. 回避方法も一応用意されてはいます。 For the vast majority of applications this change needs no action. But in the very rare event that your application needs autoloading while running in production mode, set Rails.application.config.enable_dependenc