The Initializer is responsible for processing the Rails configuration, such as setting the $LOAD_PATH, requiring the right frameworks, initializing logging, and more. It can be run either as a single command that'll just use the default configuration, like this:
But normally it's more interesting to pass in a custom configuration through the block running:
Rails::Initializer.run do |config| config.frameworks -= [ :action_web_service ] end
This will use the default configuration options from Rails::Configuration, but allow for overwriting on select areas.