The Configuration class holds all the parameters for the Initializer and ships with defaults that suites most Rails applications. But it‘s possible to overwrite everything. Usually, you‘ll create an Configuration file implicitly through the block running on the Initializer, but it‘s also possible to create the Configuration instance in advance and pass it in like this:

  config =, config)
[RW] action_controller A stub for setting options on ActionController::Base.
[RW] action_mailer A stub for setting options on ActionMailer::Base.
[RW] action_view A stub for setting options on ActionView::Base.
[RW] active_record A stub for setting options on ActiveRecord::Base.
[RW] active_resource A stub for setting options on ActiveResource::Base.
[RW] active_support A stub for setting options on ActiveSupport.
[RW] autoload_once_paths An array of paths from which Rails will automatically load from only once. All elements of this array must also be in autoload_paths.
[RW] autoload_paths An array of additional paths to prepend to the load path. By default, all app, lib, vendor and mock paths are included in this list.
[RW] cache_classes Whether or not classes should be cached (set to false if you want application classes to be reloaded on each request)
[RW] cache_store The specific cache store to use. By default, the ActiveSupport::Cache::Store will be used.
[RW] controller_paths The list of paths that should be searched for controllers. (Defaults to app/controllers.)
[RW] database_configuration_file The path to the database configuration file to use. (Defaults to config/database.yml.)
[RW] dependency_loading Enables or disables dependency loading during the request cycle. Setting dependency_loading to true will allow new classes to be loaded during a request. Setting it to false will disable this behavior.

Those who want to run in a threaded environment should disable this option and eager load or require all there classes on initialization.

If cache_classes is disabled, dependency loaded will always be on.

[RW] eager_load_paths An array of paths from which Rails will eager load on boot if cache classes is enabled. All elements of this array must also be in autoload_paths.
[RW] frameworks The list of rails framework components that should be loaded. (Defaults to :active_record, :action_controller, :action_view, :action_mailer, and :active_resource).
[RW] gems An array of gems that this rails application depends on. Rails will automatically load these gems during installation, and allow you to install any missing gems with:
  rake gems:install

You can add gems with the gem method.

[RW] i18n Accessor for i18n settings.
[RW] log_level The log level to use for the default Rails logger. In production mode, this defaults to :info. In development mode, it defaults to :debug.
[RW] log_path The path to the log file to use. Defaults to log/#{environment}.log (e.g. log/development.log or log/production.log).
[RW] logger The specific logger to use. By default, a logger will be created and initialized using log_path and log_level, but a programmer may specifically set the logger to use via this accessor and it will be used directly.
[RW] metals The list of metals to load. If this is set to nil, all metals will be loaded in alphabetical order. If this is set to [], no metals will be loaded. Otherwise metals will be loaded in the order specified
[RW] plugin_loader The class that handles loading each plugin. Defaults to Rails::Plugin::Loader, but a sub class would have access to fine grained modification of the loading behavior. See the implementation of Rails::Plugin::Loader for more details.
[RW] plugin_locators The classes that handle finding the desired plugins that you‘d like to load for your application. By default it is the Rails::Plugin::FileSystemLocator which finds plugins to load in vendor/plugins. You can hook into gem location by subclassing Rails::Plugin::Locator and adding it onto the list of plugin_locators.
[RW] plugin_paths The path to the root of the plugins directory. By default, it is in vendor/plugins.
[R] plugins The list of plugins to load. If this is set to nil, all plugins will be loaded. If this is set to [], no plugins will be loaded. Otherwise, plugins will be loaded in the order specified.
[RW] preload_frameworks Whether to preload all frameworks at startup.
[RW] reload_plugins Enables or disables plugin reloading. You can get around this setting per plugin. If reload_plugins? is false, add this to your plugin‘s init.rb to make it reloadable:
  ActiveSupport::Dependencies.autoload_once_paths.delete lib_path

If reload_plugins? is true, add this to your plugin‘s init.rb to only load it once:

  ActiveSupport::Dependencies.autoload_once_paths << lib_path
[R] root_path The application‘s base directory.
[RW] routes_configuration_file The path to the routes configuration file to use. (Defaults to config/routes.rb.)
[RW] time_zone Sets the default time_zone. Setting this will enable time_zone awareness for Active Record models and set the Active Record default timezone to :utc.
[RW] view_path The root of the application‘s views. (Defaults to app/views.)
[RW] whiny_nils Set to true if you want to be warned (noisily) when you try to invoke any method of nil. Set to false for the standard Ruby behavior.
Public Class methods

Create a new Configuration instance, initialized with the default values.

     # File railties/lib/initializer.rb, line 862
862:     def initialize
863:       set_root_path!
865:       self.frameworks                   = default_frameworks
866:       self.autoload_paths               = default_autoload_paths
867:       self.autoload_once_paths          = default_autoload_once_paths
868:       self.eager_load_paths             = default_eager_load_paths
869:       self.log_path                     = default_log_path
870:       self.log_level                    = default_log_level
871:       self.view_path                    = default_view_path
872:       self.controller_paths             = default_controller_paths
873:       self.preload_frameworks           = default_preload_frameworks
874:       self.cache_classes                = default_cache_classes
875:       self.dependency_loading           = default_dependency_loading
876:       self.whiny_nils                   = default_whiny_nils
877:       self.plugins                      = default_plugins
878:       self.plugin_paths                 = default_plugin_paths
879:       self.plugin_locators              = default_plugin_locators
880:       self.plugin_loader                = default_plugin_loader
881:       self.database_configuration_file  = default_database_configuration_file
882:       self.routes_configuration_file    = default_routes_configuration_file
883:       self.gems                         = default_gems
884:       self.i18n                         = default_i18n
886:       for framework in default_frameworks
887:         self.send("#{framework}=",
888:       end
889:       self.active_support =
890:     end
Public Instance methods

Adds a block which will be executed after rails has been fully initialized. Useful for per-environment configuration which depends on the framework being fully initialized.

     # File railties/lib/initializer.rb, line 947
947:     def after_initialize(&after_initialize_block)
948:       after_initialize_blocks << after_initialize_block if after_initialize_block
949:     end

Returns the blocks added with Configuration#after_initialize

     # File railties/lib/initializer.rb, line 952
952:     def after_initialize_blocks
953:       @after_initialize_blocks ||= []
954:     end
breakpoint_server(_ = nil)

Deprecated options:

This method is also aliased as breakpoint_server=
     # File railties/lib/initializer.rb, line 843
843:     def breakpoint_server(_ = nil)
844:       $stderr.puts %(
845:       *******************************************************************
846:       * config.breakpoint_server has been deprecated and has no effect. *
847:       *******************************************************************
848:       )
849:     end
breakpoint_server=(_ = nil)

Alias for breakpoint_server

     # File railties/lib/initializer.rb, line 972
972:     def builtin_directories
973:       # Include builtins only in the development environment.
974:       (environment == 'development') ? Dir["#{RAILTIES_PATH}/builtin/*/"] : []
975:     end

Loads and returns the contents of the database_configuration_file. The contents of the file are processed via ERB before being sent through YAML::load.

     # File railties/lib/initializer.rb, line 927
927:     def database_configuration
928:       require 'erb'
929:       YAML::load(
930:     end

Return the currently selected environment. By default, it returns the value of the RAILS_ENV constant.

     # File railties/lib/initializer.rb, line 940
940:     def environment
941:       ::RAILS_ENV
942:     end

The path to the current environment‘s file (development.rb, etc.). By default the file is at config/environments/#{environment}.rb.

     # File railties/lib/initializer.rb, line 934
934:     def environment_path
935:       "#{root_path}/config/environments/#{environment}.rb"
936:     end
     # File railties/lib/initializer.rb, line 977
977:     def framework_paths
978:       paths = %w(railties railties/lib activesupport/lib)
979:       paths << 'actionpack/lib' if frameworks.include?(:action_controller) || frameworks.include?(:action_view)
981:       [:active_record, :action_mailer, :active_resource, :action_web_service].each do |framework|
982:         paths << "#{framework.to_s.gsub('_', '')}/lib" if frameworks.include?(framework)
983:       end
985: { |dir| "#{framework_root_path}/#{dir}" }.select { |dir| }
986:     end
gem(name, options = {})

Adds a single Gem dependency to the rails application. By default, it will require the library with the same name as the gem. Use :lib to specify a different name.

  # gem 'aws-s3', '>= 0.4.0'
  # require 'aws/s3'
  config.gem 'aws-s3', :lib => 'aws/s3', :version => '>= 0.4.0',      #     :source => ""

To require a library be installed, but not attempt to load it, pass :lib => false

  config.gem 'qrp', :version => '0.4.1', :lib => false
     # File railties/lib/initializer.rb, line 838
838:     def gem(name, options = {})
839:       @gems <<, options)
840:     end

Deprecated, use autoload_once_paths.

     # File railties/lib/initializer.rb, line 721
721:     def load_once_paths
722:       $stderr.puts("config.load_once_paths is deprecated and removed in Rails 3, please use autoload_once_paths instead")
723:       autoload_once_paths
724:     end

Deprecated, use autoload_once_paths=.

     # File railties/lib/initializer.rb, line 727
727:     def load_once_paths=(paths)
728:       $stderr.puts("config.load_once_paths= is deprecated and removed in Rails 3, please use autoload_once_paths= instead")
729:       self.autoload_once_paths = paths
730:     end

Deprecated, use autoload_paths.

     # File railties/lib/initializer.rb, line 705
705:     def load_paths
706:       $stderr.puts("config.load_paths is deprecated and removed in Rails 3, please use autoload_paths instead")
707:       autoload_paths
708:     end

Deprecated, use autoload_paths=.

     # File railties/lib/initializer.rb, line 711
711:     def load_paths=(paths)
712:       $stderr.puts("config.load_paths= is deprecated and removed in Rails 3, please use autoload_paths= instead")
713:       self.autoload_paths = paths
714:     end
     # File railties/lib/initializer.rb, line 967
967:     def middleware
968:       require 'action_controller'
969:       ActionController::Dispatcher.middleware
970:     end
     # File railties/lib/initializer.rb, line 766
766:     def plugins=(plugins)
767:       @plugins = plugins.nil? ? nil : { |p| p.to_sym }
768:     end

Returns true if plugin reloading is enabled.

     # File railties/lib/initializer.rb, line 804
804:     def reload_plugins?
805:       !!@reload_plugins
806:     end

Set the root_path to RAILS_ROOT and canonicalize it.

     # File railties/lib/initializer.rb, line 893
893:     def set_root_path!
894:       raise 'RAILS_ROOT is not set' unless defined?(::RAILS_ROOT)
895:       raise 'RAILS_ROOT is not a directory' unless
897:       @root_path =
898:         # Pathname is incompatible with Windows, but Windows doesn't have
899:         # real symlinks so File.expand_path is safe.
900:         if RUBY_PLATFORM =~ /(:?mswin|mingw)/
901:           File.expand_path(::RAILS_ROOT)
903:         # Otherwise use Pathname#realpath which respects symlinks.
904:         else
906:         end
908:       Object.const_set(:RELATIVE_RAILS_ROOT, ::RAILS_ROOT.dup) unless defined?(::RELATIVE_RAILS_ROOT)
909:       ::RAILS_ROOT.replace @root_path
910:     end

Enable threaded mode. Allows concurrent requests to controller actions and multiple database connections. Also disables automatic dependency loading after boot, and disables reloading code on every request, as these are fundamentally incompatible with thread safety.

     # File railties/lib/initializer.rb, line 916
916:     def threadsafe!
917:       self.preload_frameworks = true
918:       self.cache_classes = true
919:       self.dependency_loading = false
920:       self.action_controller.allow_concurrency = true
921:       self
922:     end

Add a preparation callback that will run before every request in development mode, or before the first request in production.

See Dispatcher#to_prepare.

     # File railties/lib/initializer.rb, line 960
960:     def to_prepare(&callback)
961:       after_initialize do
962:         require 'dispatcher' unless defined?(::Dispatcher)
963:         Dispatcher.to_prepare(&callback)
964:       end
965:     end