* before_configuration: this hook is run immediately after the Application class
comes into existence, but before the user has added any configuration. This is
the appropriate place to set configuration for your plugin
* before_initialize: This is run after all of the user's configuration has completed,
but before any initializers have begun (in other words, it runs right after
config/environments/{development,production,test}.rb)
* after_initialize: This is run after all of the initializers have run. It is an
appropriate place for forking in a preforking setup
Each of these hooks may be used via ActiveSupport.on_load(name) { }. In all these cases, the context inside the block will be the Application object. This means that for simple cases, you can use these hooks without needing to create a Railtie.
Kir Shatrov