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 setup 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
[R] executor
[R] reloader
[R] reloaders
[RW] sandbox
[RW] sandbox?

Class Public methods

create(initial_variable_values = {}, &block)

📝 Source code 
# File railties/lib/rails/application.rb, line 102
      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 106
      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 91
      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 98
      def instance
        super.run_load_hooks!
      end
🔎 See on GitHub

new(initial_variable_values = {}, &block)

📝 Source code 
# File railties/lib/rails/application.rb, line 127
    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.

Example:

# 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
📝 Source code 
# File railties/lib/rails/application.rb, line 226
    def config_for(name, env: Rails.env)
      if name.is_a?(Pathname)
        yaml = name
      else
        yaml = Pathname.new("#{paths["config"].existent.first}/#{name}.yml")
      end

      if yaml.exist?
        require "erb"
        (YAML.load(ERB.new(yaml.read).result) || {})[env] || {}
      else
        raise "Could not load configuration. No such file - #{yaml}"
      end
    rescue Psych::SyntaxError => e
      raise "YAML syntax error occurred while parsing #{yaml}. " \
        "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
        "Error: #{e.message}"
    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 298
    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.

📝 Source code 
# File railties/lib/rails/application.rb, line 441
    def credentials
      @credentials ||= encrypted("config/credentials.yml.enc")
    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 bin/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 472
    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 247
    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_token" => secrets.secret_token,
          "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.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
        )
      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 304
    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 148
    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 286
    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 309
    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 172
    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 ||=
        if secret_key_base
          ActiveSupport::CachingKeyGenerator.new(
            ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
          )
        else
          ActiveSupport::LegacyKeyGenerator.new(secrets.secret_token)
        end
    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 203
    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 279
    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 167
    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 292
    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 test and development, this is simply derived as a MD5 hash of the application's name.

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 428
    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()

Returns secrets added to config/secrets.yml.

Example:

development:
  secret_key_base: 836fa3665997a860728bcb9e9a1e704d427cfc920e79d847d79c8a9a907b9e965defa4154b2b86bdec6930adbe33f21364523a6f6ce363865724549fdfc08553
test:
  secret_key_base: 5a37811464e7d378488b0f073e2193b093682e4e21f5d6f3ae0a4e1781e61a351fdc878a843424e81c73fb484a40d23f92c8dafac4870e74ede6e5e174423010
production:
  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
  namespace: my_app_production

Rails.application.secrets.namespace returns my_app_production in the production environment.

📝 Source code 
# File railties/lib/rails/application.rb, line 394
    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
        # Fallback to config.secret_token if secrets.secret_token isn't set
        secrets.secret_token ||= config.secret_token

        if secrets.secret_token.present?
          ActiveSupport::Deprecation.warn(
            "`secrets.secret_token` is deprecated in favor of `secret_key_base` and will be removed in Rails 6.0."
          )
        end

        secrets
      end
    end
🔎 See on GitHub

Instance Protected methods

validate_secret_key_base(secret_key_base)

📝 Source code 
# File railties/lib/rails/application.rb, line 579
    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`"
      elsif secrets.secret_token.blank?
        raise ArgumentError, "Missing `secret_key_base` for '#{Rails.env}' environment, set this string with `rails credentials:edit`"
      end
    end
🔎 See on GitHub