An Engine with the responsibility of coordinating the whole boot process.

Initialization

Rails::Application is responsible for executing all railties and engines initializers. It also executes some bootstrap initializers (check Rails::Application::Bootstrap) and finishing initializers, after all the others are executed (check Rails::Application::Finisher).

Configuration

Besides providing the same configuration as Rails::Engine and Rails::Railtie, the application object has several specific configurations, for example “cache_classes”, “consider_all_requests_local”, “filter_parameters”, “logger” and so forth.

Check Rails::Application::Configuration to see them all.

Routes

The application object is also responsible for holding the routes and reloading routes whenever the files change in development.

Middlewares

The Application is also responsible for building the middleware stack.

Booting process

The application is also responsible for setting up and executing the booting process. From the moment you require “config/application.rb” in your app, the booting process goes like this:

1)  require "config/boot.rb" to set up load paths
2)  require railties and engines
3)  Define Rails.application as "class MyApp::Application < Rails::Application"
4)  Run config.before_configuration callbacks
5)  Load config/environments/ENV.rb
6)  Run config.before_initialize callbacks
7)  Run Railtie#initializer defined by railties, engines and application.
    One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.
8)  Custom Railtie#initializers added by railties, engines and applications are executed
9)  Build the middleware stack and run to_prepare callbacks
10) Run config.before_eager_load and eager_load! if eager_load is true
11) Run config.after_initialize callbacks

Multiple Applications

If you decide to define multiple applications, then the first application that is initialized will be set to Rails.application, unless you override it with a different application.

To create a new application, you can instantiate a new instance of a class that has already been created:

class Application < Rails::Application
end

first_application  = Application.new
second_application = Application.new(config: first_application.config)

In the above example, the configuration from the first application was used to initialize the second application. You can also use the initialize_copy on one of the applications to create a copy of the application which shares the configuration.

If you decide to define Rake tasks, runners, or initializers in an application other than Rails.application, then you must run them manually.

Namespace

Module

Class

Methods

Attributes

[RW] assets
[W] config
[W] credentials
[R] executor
[R] reloader
[R] reloaders
[RW] sandbox
[RW] sandbox?
[W] secrets

Class Public methods

create(initial_variable_values = {}, &block)

📝 Source code 
# File railties/lib/rails/application.rb, line 103
      def create(initial_variable_values = {}, &block)
        new(initial_variable_values, &block).run_load_hooks!
      end
🔎 See on GitHub

find_root(from)

📝 Source code 
# File railties/lib/rails/application.rb, line 107
      def find_root(from)
        find_root_with_flag "config.ru", from, Dir.pwd
      end
🔎 See on GitHub

inherited(base)

📝 Source code 
# File railties/lib/rails/application.rb, line 92
      def inherited(base)
        super
        Rails.app_class = base
        add_lib_to_load_path!(find_root(base.called_from))
        ActiveSupport.run_load_hooks(:before_configuration, base)
      end
🔎 See on GitHub

instance()

📝 Source code 
# File railties/lib/rails/application.rb, line 99
      def instance
        super.run_load_hooks!
      end
🔎 See on GitHub

new(initial_variable_values = {}, &block)

📝 Source code 
# File railties/lib/rails/application.rb, line 128
    def initialize(initial_variable_values = {}, &block)
      super()
      @initialized       = false
      @reloaders         = []
      @routes_reloader   = nil
      @app_env_config    = nil
      @ordered_railties  = nil
      @railties          = nil
      @message_verifiers = {}
      @ran_load_hooks    = false

      @executor          = Class.new(ActiveSupport::Executor)
      @reloader          = Class.new(ActiveSupport::Reloader)
      @reloader.executor = @executor

      # are these actually used?
      @initial_variable_values = initial_variable_values
      @block = block
    end
🔎 See on GitHub

Instance Public methods

config_for(name, env: Rails.env)

Convenience for loading config/foo.yml for the current Rails env.

Examples:

# config/exception_notification.yml:
production:
  url: http://127.0.0.1:8080
  namespace: my_app_production

development:
  url: http://localhost:3001
  namespace: my_app_development

# config/environments/production.rb
Rails.application.configure do
  config.middleware.use ExceptionNotifier, config_for(:exception_notification)
end

# You can also store configurations in a shared section which will be
# merged with the environment configuration

# config/example.yml
shared:
  foo:
    bar:
      baz: 1

development:
  foo:
    bar:
      qux: 2

# development environment
Rails.application.config_for(:example)[:foo][:bar]
# => { baz: 1, qux: 2 }
📝 Source code 
# File railties/lib/rails/application.rb, line 241
    def config_for(name, env: Rails.env)
      yaml = name.is_a?(Pathname) ? name : Pathname.new("#{paths["config"].existent.first}/#{name}.yml")

      if yaml.exist?
        require "erb"
        all_configs    = ActiveSupport::ConfigurationFile.parse(yaml).deep_symbolize_keys
        config, shared = all_configs[env.to_sym], all_configs[:shared]

        if shared
          config = {} if config.nil?
          if config.is_a?(Hash)
            config = shared.deep_merge(config)
          end
        end

        if config.is_a?(Hash)
          config = ActiveSupport::OrderedOptions.new.update(config)
        end

        config
      else
        raise "Could not load configuration. No such file - #{yaml}"
      end
    end
🔎 See on GitHub

console(&blk)

Sends any console called in the instance of a new application up to the console method defined in Rails::Railtie.

📝 Source code 
# File railties/lib/rails/application.rb, line 322
    def console(&blk)
      self.class.console(&blk)
    end
🔎 See on GitHub

credentials()

Decrypts the credentials hash as kept in config/credentials.yml.enc. This file is encrypted with the Rails master key, which is either taken from ENV["RAILS_MASTER_KEY"] or from loading config/master.key. If specific credentials file exists for current environment, it takes precedence, thus for production environment look first for config/credentials/production.yml.enc with master key taken from ENV["RAILS_MASTER_KEY"] or from loading config/credentials/production.key. Default behavior can be overwritten by setting config.credentials.content_path and config.credentials.key_path.

📝 Source code 
# File railties/lib/rails/application.rb, line 450
    def credentials
      @credentials ||= encrypted(config.credentials.content_path, key_path: config.credentials.key_path)
    end
🔎 See on GitHub

eager_load!()

Eager loads the application code.

📝 Source code 
# File railties/lib/rails/application.rb, line 515
    def eager_load!
      if Rails.autoloaders.zeitwerk_enabled?
        Rails.autoloaders.each(&:eager_load)
      else
        super
      end
    end
🔎 See on GitHub

encrypted(path, key_path: "config/master.key", env_key: "RAILS_MASTER_KEY")

Shorthand to decrypt any encrypted configurations or files.

For any file added with rails encrypted:edit call read to decrypt the file with the master key. The master key is either stored in config/master.key or ENV["RAILS_MASTER_KEY"].

Rails.application.encrypted("config/mystery_man.txt.enc").read
# => "We've met before, haven't we?"

It's also possible to interpret encrypted YAML files with config.

Rails.application.encrypted("config/credentials.yml.enc").config
# => { next_guys_line: "I don't think so. Where was it you think we met?" }

Any top-level configs are also accessible directly on the return value:

Rails.application.encrypted("config/credentials.yml.enc").next_guys_line
# => "I don't think so. Where was it you think we met?"

The files or configs can also be encrypted with a custom key. To decrypt with a key in the ENV, use:

Rails.application.encrypted("config/special_tokens.yml.enc", env_key: "SPECIAL_TOKENS")

Or to decrypt with a file, that should be version control ignored, relative to Rails.root:

Rails.application.encrypted("config/special_tokens.yml.enc", key_path: "config/special_tokens.key")
📝 Source code 
# File railties/lib/rails/application.rb, line 481
    def encrypted(path, key_path: "config/master.key", env_key: "RAILS_MASTER_KEY")
      ActiveSupport::EncryptedConfiguration.new(
        config_path: Rails.root.join(path),
        key_path: Rails.root.join(key_path),
        env_key: env_key,
        raise_if_missing_key: config.require_master_key
      )
    end
🔎 See on GitHub

env_config()

Stores some of the Rails initial environment parameters which will be used by middlewares and engines to configure themselves.

📝 Source code 
# File railties/lib/rails/application.rb, line 268
    def env_config
      @app_env_config ||= begin
        super.merge(
          "action_dispatch.parameter_filter" => config.filter_parameters,
          "action_dispatch.redirect_filter" => config.filter_redirect,
          "action_dispatch.secret_key_base" => secret_key_base,
          "action_dispatch.show_exceptions" => config.action_dispatch.show_exceptions,
          "action_dispatch.show_detailed_exceptions" => config.consider_all_requests_local,
          "action_dispatch.logger" => Rails.logger,
          "action_dispatch.backtrace_cleaner" => Rails.backtrace_cleaner,
          "action_dispatch.key_generator" => key_generator,
          "action_dispatch.http_auth_salt" => config.action_dispatch.http_auth_salt,
          "action_dispatch.signed_cookie_salt" => config.action_dispatch.signed_cookie_salt,
          "action_dispatch.encrypted_cookie_salt" => config.action_dispatch.encrypted_cookie_salt,
          "action_dispatch.encrypted_signed_cookie_salt" => config.action_dispatch.encrypted_signed_cookie_salt,
          "action_dispatch.authenticated_encrypted_cookie_salt" => config.action_dispatch.authenticated_encrypted_cookie_salt,
          "action_dispatch.use_authenticated_cookie_encryption" => config.action_dispatch.use_authenticated_cookie_encryption,
          "action_dispatch.encrypted_cookie_cipher" => config.action_dispatch.encrypted_cookie_cipher,
          "action_dispatch.signed_cookie_digest" => config.action_dispatch.signed_cookie_digest,
          "action_dispatch.cookies_serializer" => config.action_dispatch.cookies_serializer,
          "action_dispatch.cookies_digest" => config.action_dispatch.cookies_digest,
          "action_dispatch.cookies_rotations" => config.action_dispatch.cookies_rotations,
          "action_dispatch.cookies_same_site_protection" => coerce_same_site_protection(config.action_dispatch.cookies_same_site_protection),
          "action_dispatch.use_cookies_with_metadata" => config.action_dispatch.use_cookies_with_metadata,
          "action_dispatch.content_security_policy" => config.content_security_policy,
          "action_dispatch.content_security_policy_report_only" => config.content_security_policy_report_only,
          "action_dispatch.content_security_policy_nonce_generator" => config.content_security_policy_nonce_generator,
          "action_dispatch.content_security_policy_nonce_directives" => config.content_security_policy_nonce_directives,
          "action_dispatch.permissions_policy" => config.permissions_policy,
        )
      end
    end
🔎 See on GitHub

generators(&blk)

Sends any generators called in the instance of a new application up to the generators method defined in Rails::Railtie.

📝 Source code 
# File railties/lib/rails/application.rb, line 328
    def generators(&blk)
      self.class.generators(&blk)
    end
🔎 See on GitHub

initialized?()

Returns true if the application is initialized.

📝 Source code 
# File railties/lib/rails/application.rb, line 149
    def initialized?
      @initialized
    end
🔎 See on GitHub

initializer(name, opts = {}, &block)

Sends the initializers to the initializer method defined in the Rails::Initializable module. Each Rails::Application class has its own set of initializers, as defined by the Initializable module.

📝 Source code 
# File railties/lib/rails/application.rb, line 310
    def initializer(name, opts = {}, &block)
      self.class.initializer(name, opts, &block)
    end
🔎 See on GitHub

isolate_namespace(mod)

Sends the isolate_namespace method up to the class method.

📝 Source code 
# File railties/lib/rails/application.rb, line 339
    def isolate_namespace(mod)
      self.class.isolate_namespace(mod)
    end
🔎 See on GitHub

key_generator()

Returns the application's KeyGenerator

📝 Source code 
# File railties/lib/rails/application.rb, line 173
    def key_generator
      # number of iterations selected based on consultation with the google security
      # team. Details at https://github.com/rails/rails/pull/6952#issuecomment-7661220
      @caching_key_generator ||= ActiveSupport::CachingKeyGenerator.new(
        ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
      )
    end
🔎 See on GitHub

message_verifier(verifier_name)

Returns a message verifier object.

This verifier can be used to generate and verify signed messages in the application.

It is recommended not to use the same verifier for different things, so you can get different verifiers passing the verifier_name argument.

Parameters

  • verifier_name - the name of the message verifier.

Examples

message = Rails.application.message_verifier('sensitive_data').generate('my sensible data')
Rails.application.message_verifier('sensitive_data').verify(message)
# => 'my sensible data'

See the ActiveSupport::MessageVerifier documentation for more information.

📝 Source code 
# File railties/lib/rails/application.rb, line 199
    def message_verifier(verifier_name)
      @message_verifiers[verifier_name] ||= begin
        secret = key_generator.generate_key(verifier_name.to_s)
        ActiveSupport::MessageVerifier.new(secret)
      end
    end
🔎 See on GitHub

rake_tasks(&block)

If you try to define a set of Rake tasks on the instance, these will get passed up to the Rake tasks defined on the application's class.

📝 Source code 
# File railties/lib/rails/application.rb, line 303
    def rake_tasks(&block)
      self.class.rake_tasks(&block)
    end
🔎 See on GitHub

reload_routes!()

Reload application routes regardless if they changed or not.

📝 Source code 
# File railties/lib/rails/application.rb, line 168
    def reload_routes!
      routes_reloader.reload!
    end
🔎 See on GitHub

runner(&blk)

Sends any runner called in the instance of a new application up to the runner method defined in Rails::Railtie.

📝 Source code 
# File railties/lib/rails/application.rb, line 316
    def runner(&blk)
      self.class.runner(&blk)
    end
🔎 See on GitHub

secret_key_base()

The secret_key_base is used as the input secret to the application's key generator, which in turn is used to create all MessageVerifiers/MessageEncryptors, including the ones that sign and encrypt cookies.

In development and test, this is randomly generated and stored in a temporary file in tmp/development_secret.txt.

In all other environments, we look for it first in ENV, then credentials.secret_key_base, and finally secrets.secret_key_base. For most applications, the correct place to store it is in the encrypted credentials file.

📝 Source code 
# File railties/lib/rails/application.rb, line 433
    def secret_key_base
      if Rails.env.development? || Rails.env.test?
        secrets.secret_key_base ||= generate_development_secret
      else
        validate_secret_key_base(
          ENV["SECRET_KEY_BASE"] || credentials.secret_key_base || secrets.secret_key_base
        )
      end
    end
🔎 See on GitHub

secrets()

📝 Source code 
# File railties/lib/rails/application.rb, line 408
    def secrets
      @secrets ||= begin
        secrets = ActiveSupport::OrderedOptions.new
        files = config.paths["config/secrets"].existent
        files = files.reject { |path| path.end_with?(".enc") } unless config.read_encrypted_secrets
        secrets.merge! Rails::Secrets.parse(files, env: Rails.env)

        # Fallback to config.secret_key_base if secrets.secret_key_base isn't set
        secrets.secret_key_base ||= config.secret_key_base

        secrets
      end
    end
🔎 See on GitHub

server(&blk)

Sends any server called in the instance of a new application up to the server method defined in Rails::Railtie.

📝 Source code 
# File railties/lib/rails/application.rb, line 334
    def server(&blk)
      self.class.server(&blk)
    end
🔎 See on GitHub

Instance Protected methods

validate_secret_key_base(secret_key_base)

📝 Source code 
# File railties/lib/rails/application.rb, line 597
    def validate_secret_key_base(secret_key_base)
      if secret_key_base.is_a?(String) && secret_key_base.present?
        secret_key_base
      elsif secret_key_base
        raise ArgumentError, "`secret_key_base` for #{Rails.env} environment must be a type of String`"
      else
        raise ArgumentError, "Missing `secret_key_base` for '#{Rails.env}' environment, set this string with `bin/rails credentials:edit`"
      end
    end
🔎 See on GitHub