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Configurando Aplicações Rails

Este guia cobre as configurações e funcionalidades de inicialização disponíveis para aplicações Rails.

Após ler esse guia, você vai saber:

1 Locais para Código de Inicialização

O Rails oferece quatro opções padrão para adicionar código para a inicialização:

  • config/application.rb
  • Arquivos de configuração específicos para os ambientes
  • Initializers
  • Pós initializers

2 Executando Código Antes do Rails

Em raras situações em que sua aplicação necessita executar código antes que o próprio Rails tenha sido carregado, coloque este código acima da chamada require 'rails/all' no arquivo config/application.rb.

3 Configurando Componentes Rails

Em geral, o ato de configurar o Rails significa configurar os componentes do Rails, assim como configurar o Rails em si. O arquivo de configuração config/application.rb e arquivos de configuração específicos de ambiente (como o arquivo config/environments/production.rb) permitem definir diversas configurações que serão passadas para todos os componentes.

Por exemplo, você pode adicionar a configuração abaixo ao arquivo config/application.rb:

config.time_zone = 'Brasilia'

Essa é uma configuração para o próprio Rails. Se você deseja definir ajustes para componentes do Rails, você pode fazê-lo através do mesmo objeto config em config/application.rb:

config.active_record.schema_format = :ruby

O Rails vai usar essa configuração em particular no Active Record.

3.1 Configuração Geral do Rails

Esses métodos de configuração devem ser enviados para objetos do tipo Rails::Railtie, como uma subclasse de Rails::Engine ou Rails::Application.

  • config.after_initialize recebe um bloco que será executado após a inicialização da aplicação Rails. Isso inclui a inicialização do framework em si, engines e todos initializers definidos em config/initializers. Perceba que esse bloco será executado em tarefas rake. Essa opção é útil para configurações feitas por outros initializers:
config.after_initialize do
  ActionView::Base.sanitized_allowed_tags.delete 'div'
end

  • config.asset_host define o host para os assets. Essa opção é útil quando CDNs são usados para hospedar assets, ou para quando você deseja contornar restrições de concorrência embutidas em navegadores usando diferentes aliases de domínios. Essa é uma versão encurtada de config.action_controller.asset_host.

  • config.autoload_once_paths aceita um array de caminhos de onde o Rails deve carregar automaticamente constantes que não serão removidas por uma requisição. Essa configuração é relevante se config.cache_classes está definido como false, que é o padrão no modo de desenvolvimento. De outra forma, todo auto carregamento acontece somente uma vez. Todos elementos desse array devem estar também em autoload_paths. O valor padrão é um array vazio.

  • config.autoload_paths aceita um array de caminhos de onde o Rails deve carregar automaticamente constantes. O padrão são todos diretórios abaixo de app. Não é mais recomendado ajustar essa configuração. Veja mais em Auto carregamento e Recarregando Constantes

  • config.add_autoload_paths_to_load_path determina se os caminhos de auto carregamento devem ser adicionados para $LOAD_PATH. Esta configuração é true por padrão, mas é recomendado que seja definida como false no recém lançado modo :zeitwerk, em config/application.rb. O modo Zeitwerk usa caminhos absolutos internamente e aplicações executadas neste modo não necessitam de require_dependency, então models, controllers, jobs, etc não precisam estar no $LOAD_PATH. Ao ser definido como false, previne o Ruby de verificar estes diretórios quando resolver chamadas de require com caminhos relativos e reduz o processamento e o consumo de memória RAM do Bootsnap, já que ele não precisa construir um índice para eles.

  • config.cache_classes controla quando as classes e módulos da aplicação devem ser recarregados em caso de mudanças. O padrão é false no modo desenvolvimento e true no modo de produção. No modo de test, o padrão é false se o Spring estiver instalado, caso contrário é true.

  • config.beginning_of_week configura o começo da semana para a aplicação. O valor deve ser um symbol com um dia da semana válido (por ex: :monday).

  • config.cache_store configura qual armazenamento de cache o Rails deve utilizar. As opções incluem um dos symbols: :memory_store, :file_store, :mem_cache_store, :null_store, :redis_cache_store, ou um objeto que implementa a API de cache. O padrão é :file_store.

  • config.colorize_logging determina quando utilizar ou não códigos de cores ANSI ao registrar informações no log. O padrão é true.

  • config.consider_all_requests_local quando true adiciona informações detalhadas de debug de erros à resposta HTTP, e o controller Rails::Info irá exibir o contexto de execução da aplicação em /rails/info/properties. true é o padrão nos ambientes de desenvolvimento e teste e false é o padrão no modo de produção. Para um controle mais refinado, defina como false e implemente o método local_request? em seus controllers para especificar que requisições devem prover informações de debug em erros.

  • config.console permite que você defina qual classe deve ser usada quando executar rails console. É melhor que seja executada dentre de um bloco console:

    console do
      # este bloco só é chamado quando o console estiver executando,
      # então podemos requerer o pry de forma segura
      require "pry"
      config.console = Pry
    end
    
    
  • config.disable_sandbox controla se o console pode ser iniciado ou não no modo sandbox. Esta configuração é útil para evitar sessões muito longas de console em modo sandbox, o que poderia levar o servidor de banco de dados a ficar sem memória. O padrão é false.

  • config.eager_load quando true, todos namespaces definidos em config.eager_load_namespaces são carregados de forma ativa (eager load). Isto inclui a sua aplicação, engines, frameworks do Rails e qualquer outra namespace definida.

  • config.eager_load_namespaces define todas namespaces que serão carregadas ativamente (eager load) quando config.eager_load estiver definido como true. Todas namespaces na lista devem responder ao método eager_load!.

  • config.eager_load_paths recebe um array de caminhos de onde o Rails deve carregar ativamente durante a inicialização se o cache de classes está ativo. O padrão são todas as pastas dentro do diretório app.

  • config.enable_dependency_loading: quando definido como true, habilita o autocarregamento mesmo que a aplicação esteja carregada ativamente (eager load) e que config.cache_classes esteja definido como true. O padrão é false

  • config.encoding define o encoding para toda a aplicação. O padrão é UTF-8.

  • config.exceptions_app define a aplicação invocada pelo middleware ShowException quando uma exceção acontece. O padrão é ActionDispatch::PublicExceptions.new(Rails.public_path).

  • config.debug_exception_response_format define o formato usado nas respostas quando errors acontecem em modo desenvolvimento. O padrão é :api para aplicações somente API e :default para aplicações regulares.

  • config.file_watcher é a classe usada para detectar atualizações nos arquivos quando config.reload_classes_only_on_change está definido como true. Rails é distribuído com a classe ActiveSupport::FileUpdateChecker, que é o padrão, e com ActiveSupport::EventedFileUpdateChecker (que depende da gem listen). Classes customizadas devem respeitar a API de ActiveSupport::FileUpdateChecker.

  • config.filter_parameters é usado para filtrar os parâmetros que você não deseja exibir nos logs, tais como senhas ou números de cartões de crédito. Essa configuração também filtra valores sensíveis de colunas de bancos de dados quando o método #inspect é enviado a um objeto de Active Record. Por padrão o Rails filtra senhas ao adicionar Rails.application.config.filter_parameters += [:password] em config/initializers/filter_parameter_logging.rb. O filtro de parâmetros funciona através da equivalência parcial de expressões regulares.

  • config.force_ssl impõe que todas requisições sejam tratadas através de HTTPS utilizando o middleware ActionDispatch::SSL, e define o valor de config.action_mailer.default_url_options como { protocol: 'https' }. Essa configuração pode ser feita através de config.ssl_options - veja a documentação de ActionDispatch::SSL para mais detalhes.

  • config.log_formatter define o formatador do logger do Rails. O valor padrão é uma instância de ActiveSupport::Logger::SimpleFormatter para todos os modos. Se você definir um valor para config.logger você deve enviar o valor do seu formatador manualmente, antes que ele seja acondicionado em uma instância de ActiveSupport::TaggedLogging, o Rails não fará isso por você.

  • config.log_level define a verbosidade do logger do Rails. O padrão dessa opção é :debug para todos ambientes. Os níveis disponíveis são :debug, :info, :warn, :error, :fatal, e :unknown.

  • config.log_tags aceita uma lista de: mmétodos que o objeto request responde, uma Proc que aceita um objeto de request, ou algo que responda ao método to_s. Isto torna fácil adicionar linhas ao log com informações sobre o debug, como subdomínios e ids de requisições - ambos muito úteis para debugar aplicações multi-usuário em produção.

  • config.logger é o logger que será usado pelo Rails.logger e qualquer outro log relacionado ao Rails, tal como ActiveRecord::Base.logger. O padrão é uma instância de ActiveSupport::TaggedLogging que envolve uma instância de ActiveSupport::Logger, que registra a saída do log no diretório log/. Você pode informar um logger personalizado mas para obter compatibilidade total você deve seguir esses requisitos:

    • Para suportar um formatador, você deve atribuir manualmente o formatador definido em config.log_formatter para o logger.
    • Para suportar logs com etiquetaas (tags), a instância do log deve ser envolvida com ActiveSupport::TaggedLogging
    • Para suportar o silenciamento, o logger deve incluir o módulo ActiveSupport::LoggerSilence. A classe ActiveSupport::Logger já inclui esse módulo.
    class MyLogger < ::Logger
      include ActiveSupport::LoggerSilence
    end
    
    mylogger           = MyLogger.new(STDOUT)
    mylogger.formatter = config.log_formatter
    config.logger      = ActiveSupport::TaggedLogging.new(mylogger)
    
    
  • config.middleware permite configurar o middleware da aplicação. Esse tópico é coberto em detalhes em Configurando o Middleware.

  • config.reload_classes_only_on_change habilita ou desabilita a recarga de classes somente quando arquivos monitorados são modificados. Por padrão são monitorados todos caminhos de auto carregamento (autoload). Se config.cache_classes está definido como true essa opção é ignorada.

  • config.credentials.content_path configura o caminho para busca por credenciais criptografadas.

  • config.credentials.key_path configura o caminho para busca por chaves de criptografia.

  • secret_key_base é usado para especificar uma chave que permite que sessões da aplicação sejam verificadas contra uma chave segura conhecida prevenindo falsificações (tampering). Aplicações recebem uma chave gerada aleatoriamente nos ambientes de desenvolvimento e teste, outros ambientes devem definir uma chave em config/credentials.yml.enc.

  • config.public_file_server.enabled configura o Rails para servir arquivos estáticos a partir do diretório public. O padrão é true, mas no ambiente de produção é definido como false porque o software servidor (como NGINX ou Apache) usado para executar a aplicação deve servir os arquivos estáticos. Se você esta executando ou testando sua aplicação no modo de produção usando WEBrick (não é recomendado usar WEBrick em produção) defina a opção como true. De outra forma, você não será capaz de usar o cacheamento de páginas e requisições para arquivos que existam no diretório public.

  • config.session_store define que classe usar para armazenar a sessão. Os valores possíveis são :cookie_store, que é o padrão, :mem_cache_store e :disabled. O último indica que o Rails não deve tratar de sessões. O padrão armazena cookies com o nome da aplicação como a chave da sessão. Armazenadores personalizados de sessão também podem ser definidos:

    config.session_store :my_custom_store
    
    

    Esse armazenador personalizado deve ser definido como ActionDispatch::Session::MyCustomStore.

  • config.time_zone define o fuso horário para a aplicação e torna o Active Record ciente deste fuso horário.

  • config.autoloader configura o modo de autocarregamento. O padrão é :zeitwerk se em config.load_defaults o valor for 6.0. Aplicações ainda podem usar o autocarregador clássico ao definir o valor dessa configuração como :classic após carregar os valores padrões do framework:

    config.load_defaults "6.0"
    config.autoloader = :classic
    
    

3.2 Configuring Assets

  • config.assets.enabled a flag that controls whether the asset pipeline is enabled. It is set to true by default.

  • config.assets.css_compressor defines the CSS compressor to use. It is set by default by sass-rails. The unique alternative value at the moment is :yui, which uses the yui-compressor gem.

  • config.assets.js_compressor defines the JavaScript compressor to use. Possible values are :closure, :uglifier and :yui which require the use of the closure-compiler, uglifier or yui-compressor gems respectively.

  • config.assets.gzip a flag that enables the creation of gzipped version of compiled assets, along with non-gzipped assets. Set to true by default.

  • config.assets.paths contains the paths which are used to look for assets. Appending paths to this configuration option will cause those paths to be used in the search for assets.

  • config.assets.precompile allows you to specify additional assets (other than application.css and application.js) which are to be precompiled when rake assets:precompile is run.

  • config.assets.unknown_asset_fallback allows you to modify the behavior of the asset pipeline when an asset is not in the pipeline, if you use sprockets-rails 3.2.0 or newer. Defaults to false.

  • config.assets.prefix defines the prefix where assets are served from. Defaults to /assets.

  • config.assets.manifest defines the full path to be used for the asset precompiler's manifest file. Defaults to a file named manifest-<random>.json in the config.assets.prefix directory within the public folder.

  • config.assets.digest enables the use of SHA256 fingerprints in asset names. Set to true by default.

  • config.assets.debug disables the concatenation and compression of assets. Set to true by default in development.rb.

  • config.assets.version is an option string that is used in SHA256 hash generation. This can be changed to force all files to be recompiled.

  • config.assets.compile is a boolean that can be used to turn on live Sprockets compilation in production.

  • config.assets.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class. Defaults to the same configured at config.logger. Setting config.assets.logger to false will turn off served assets logging.

  • config.assets.quiet disables logging of assets requests. Set to true by default in development.rb.

3.3 Configuring Generators

Rails allows you to alter what generators are used with the config.generators method. This method takes a block:

config.generators do |g|
  g.orm :active_record
  g.test_framework :test_unit
end

The full set of methods that can be used in this block are as follows:

  • assets allows to create assets on generating a scaffold. Defaults to true.
  • force_plural allows pluralized model names. Defaults to false.
  • helper defines whether or not to generate helpers. Defaults to true.
  • integration_tool defines which integration tool to use to generate integration tests. Defaults to :test_unit.
  • system_tests defines which integration tool to use to generate system tests. Defaults to :test_unit.
  • orm defines which orm to use. Defaults to false and will use Active Record by default.
  • resource_controller defines which generator to use for generating a controller when using rails generate resource. Defaults to :controller.
  • resource_route defines whether a resource route definition should be generated or not. Defaults to true.
  • scaffold_controller different from resource_controller, defines which generator to use for generating a scaffolded controller when using rails generate scaffold. Defaults to :scaffold_controller.
  • stylesheets turns on the hook for stylesheets in generators. Used in Rails for when the scaffold generator is run, but this hook can be used in other generates as well. Defaults to true.
  • stylesheet_engine configures the stylesheet engine (for eg. sass) to be used when generating assets. Defaults to :css.
  • scaffold_stylesheet creates scaffold.css when generating a scaffolded resource. Defaults to true.
  • test_framework defines which test framework to use. Defaults to false and will use minitest by default.
  • template_engine defines which template engine to use, such as ERB or Haml. Defaults to :erb.

3.4 Configuring Middleware

Every Rails application comes with a standard set of middleware which it uses in this order in the development environment:

  • ActionDispatch::SSL forces every request to be served using HTTPS. Enabled if config.force_ssl is set to true. Options passed to this can be configured by setting config.ssl_options.
  • ActionDispatch::Static is used to serve static assets. Disabled if config.public_file_server.enabled is false. Set config.public_file_server.index_name if you need to serve a static directory index file that is not named index. For example, to serve main.html instead of index.html for directory requests, set config.public_file_server.index_name to "main".
  • ActionDispatch::Executor allows thread safe code reloading. Disabled if config.allow_concurrency is false, which causes Rack::Lock to be loaded. Rack::Lock wraps the app in mutex so it can only be called by a single thread at a time.
  • ActiveSupport::Cache::Strategy::LocalCache serves as a basic memory backed cache. This cache is not thread safe and is intended only for serving as a temporary memory cache for a single thread.
  • Rack::Runtime sets an X-Runtime header, containing the time (in seconds) taken to execute the request.
  • Rails::Rack::Logger notifies the logs that the request has begun. After request is complete, flushes all the logs.
  • ActionDispatch::ShowExceptions rescues any exception returned by the application and renders nice exception pages if the request is local or if config.consider_all_requests_local is set to true. If config.action_dispatch.show_exceptions is set to false, exceptions will be raised regardless.
  • ActionDispatch::RequestId makes a unique X-Request-Id header available to the response and enables the ActionDispatch::Request#uuid method.
  • ActionDispatch::RemoteIp checks for IP spoofing attacks and gets valid client_ip from request headers. Configurable with the config.action_dispatch.ip_spoofing_check, and config.action_dispatch.trusted_proxies options.
  • Rack::Sendfile intercepts responses whose body is being served from a file and replaces it with a server specific X-Sendfile header. Configurable with config.action_dispatch.x_sendfile_header.
  • ActionDispatch::Callbacks runs the prepare callbacks before serving the request.
  • ActionDispatch::Cookies sets cookies for the request.
  • ActionDispatch::Session::CookieStore is responsible for storing the session in cookies. An alternate middleware can be used for this by changing the config.action_controller.session_store to an alternate value. Additionally, options passed to this can be configured by using config.action_controller.session_options.
  • ActionDispatch::Flash sets up the flash keys. Only available if config.action_controller.session_store is set to a value.
  • Rack::MethodOverride allows the method to be overridden if params[:_method] is set. This is the middleware which supports the PATCH, PUT, and DELETE HTTP method types.
  • Rack::Head converts HEAD requests to GET requests and serves them as so.

Besides these usual middleware, you can add your own by using the config.middleware.use method:

config.middleware.use Magical::Unicorns

This will put the Magical::Unicorns middleware on the end of the stack. You can use insert_before if you wish to add a middleware before another.

config.middleware.insert_before Rack::Head, Magical::Unicorns

Or you can insert a middleware to exact position by using indexes. For example, if you want to insert Magical::Unicorns middleware on top of the stack, you can do it, like so:

config.middleware.insert_before 0, Magical::Unicorns

There's also insert_after which will insert a middleware after another:

config.middleware.insert_after Rack::Head, Magical::Unicorns

Middlewares can also be completely swapped out and replaced with others:

config.middleware.swap ActionController::Failsafe, Lifo::Failsafe

They can also be removed from the stack completely:

config.middleware.delete Rack::MethodOverride

3.5 Configuring i18n

All these configuration options are delegated to the I18n library.

  • config.i18n.available_locales defines the permitted available locales for the app. Defaults to all locale keys found in locale files, usually only :en on a new application.

  • config.i18n.default_locale sets the default locale of an application used for i18n. Defaults to :en.

  • config.i18n.enforce_available_locales ensures that all locales passed through i18n must be declared in the available_locales list, raising an I18n::InvalidLocale exception when setting an unavailable locale. Defaults to true. It is recommended not to disable this option unless strongly required, since this works as a security measure against setting any invalid locale from user input.

  • config.i18n.load_path sets the path Rails uses to look for locale files. Defaults to config/locales/*.{yml,rb}.

  • config.i18n.fallbacks sets fallback behavior for missing translations. Here are 3 usage examples for this option:

    • You can set the option to true for using default locale as fallback, like so:
    config.i18n.fallbacks = true
    
    
    • Or you can set an array of locales as fallback, like so:
    config.i18n.fallbacks = [:tr, :en]
    
    
    • Or you can set different fallbacks for locales individually. For example, if you want to use :tr for :az and :de, :en for :da as fallbacks, you can do it, like so:
    config.i18n.fallbacks = { az: :tr, da: [:de, :en] }
    #or
    config.i18n.fallbacks.map = { az: :tr, da: [:de, :en] }
    
    

3.6 Configuring Active Model

  • config.active_model.i18n_customize_full_message is a boolean value which controls whether the full_message error format can be overridden at the attribute or model level in the locale files. This is false by default.

3.7 Configuring Active Record

config.active_record includes a variety of configuration options:

  • config.active_record.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then passed on to any new database connections made. You can retrieve this logger by calling logger on either an Active Record model class or an Active Record model instance. Set to nil to disable logging.

  • config.active_record.primary_key_prefix_type lets you adjust the naming for primary key columns. By default, Rails assumes that primary key columns are named id (and this configuration option doesn't need to be set.) There are two other choices:

    • :table_name would make the primary key for the Customer class customerid.
    • :table_name_with_underscore would make the primary key for the Customer class customer_id.
  • config.active_record.table_name_prefix lets you set a global string to be prepended to table names. If you set this to northwest_, then the Customer class will look for northwest_customers as its table. The default is an empty string.

  • config.active_record.table_name_suffix lets you set a global string to be appended to table names. If you set this to _northwest, then the Customer class will look for customers_northwest as its table. The default is an empty string.

  • config.active_record.schema_migrations_table_name lets you set a string to be used as the name of the schema migrations table.

  • config.active_record.internal_metadata_table_name lets you set a string to be used as the name of the internal metadata table.

  • config.active_record.protected_environments lets you set an array of names of environments where destructive actions should be prohibited.

  • config.active_record.pluralize_table_names specifies whether Rails will look for singular or plural table names in the database. If set to true (the default), then the Customer class will use the customers table. If set to false, then the Customer class will use the customer table.

  • config.active_record.default_timezone determines whether to use Time.local (if set to :local) or Time.utc (if set to :utc) when pulling dates and times from the database. The default is :utc.

  • config.active_record.schema_format controls the format for dumping the database schema to a file. The options are :ruby (the default) for a database-independent version that depends on migrations, or :sql for a set of (potentially database-dependent) SQL statements.

  • config.active_record.error_on_ignored_order specifies if an error should be raised if the order of a query is ignored during a batch query. The options are true (raise error) or false (warn). Default is false.

  • config.active_record.timestamped_migrations controls whether migrations are numbered with serial integers or with timestamps. The default is true, to use timestamps, which are preferred if there are multiple developers working on the same application.

  • config.active_record.lock_optimistically controls whether Active Record will use optimistic locking and is true by default.

  • config.active_record.cache_timestamp_format controls the format of the timestamp value in the cache key. Default is :usec.

  • config.active_record.record_timestamps is a boolean value which controls whether or not timestamping of create and update operations on a model occur. The default value is true.

  • config.active_record.partial_writes is a boolean value and controls whether or not partial writes are used (i.e. whether updates only set attributes that are dirty). Note that when using partial writes, you should also use optimistic locking config.active_record.lock_optimistically since concurrent updates may write attributes based on a possibly stale read state. The default value is true.

  • config.active_record.maintain_test_schema is a boolean value which controls whether Active Record should try to keep your test database schema up-to-date with db/schema.rb (or db/structure.sql) when you run your tests. The default is true.

  • config.active_record.dump_schema_after_migration is a flag which controls whether or not schema dump should happen (db/schema.rb or db/structure.sql) when you run migrations. This is set to false in config/environments/production.rb which is generated by Rails. The default value is true if this configuration is not set.

  • config.active_record.dump_schemas controls which database schemas will be dumped when calling db:structure:dump. The options are :schema_search_path (the default) which dumps any schemas listed in schema_search_path, :all which always dumps all schemas regardless of the schema_search_path, or a string of comma separated schemas.

  • config.active_record.belongs_to_required_by_default is a boolean value and controls whether a record fails validation if belongs_to association is not present.

  • config.active_record.warn_on_records_fetched_greater_than allows setting a warning threshold for query result size. If the number of records returned by a query exceeds the threshold, a warning is logged. This can be used to identify queries which might be causing a memory bloat.

  • config.active_record.index_nested_attribute_errors allows errors for nested has_many relationships to be displayed with an index as well as the error. Defaults to false.

  • config.active_record.use_schema_cache_dump enables users to get schema cache information from db/schema_cache.yml (generated by rails db:schema:cache:dump), instead of having to send a query to the database to get this information. Defaults to true.

  • config.active_record.collection_cache_versioning enables the same cache key to be reused when the object being cached of type ActiveRecord::Relation changes by moving the volatile information (max updated at and count) of the relation's cache key into the cache version to support recycling cache key. Defaults to false.

The MySQL adapter adds one additional configuration option:

  • ActiveRecord::ConnectionAdapters::Mysql2Adapter.emulate_booleans controls whether Active Record will consider all tinyint(1) columns as booleans. Defaults to true.

The PostgreSQL adapter adds one additional configuration option:

  • ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables controls whether database tables created should be "unlogged," which can speed up performance but adds a risk of data loss if the database crashes. It is highly recommended that you do not enable this in a production environment. Defaults to false in all environments.

The schema dumper adds two additional configuration options:

  • ActiveRecord::SchemaDumper.ignore_tables accepts an array of tables that should not be included in any generated schema file.

  • ActiveRecord::SchemaDumper.fk_ignore_pattern allows setting a different regular expression that will be used to decide whether a foreign key's name should be dumped to db/schema.rb or not. By default, foreign key names starting with fk_rails_ are not exported to the database schema dump. Defaults to /^fk_rails_[0-9a-f]{10}$/.

3.8 Configuring Action Controller

config.action_controller includes a number of configuration settings:

  • config.action_controller.asset_host sets the host for the assets. Useful when CDNs are used for hosting assets rather than the application server itself.

  • config.action_controller.perform_caching configures whether the application should perform the caching features provided by the Action Controller component or not. Set to false in development mode, true in production. If it's not specified, the default will be true.

  • config.action_controller.default_static_extension configures the extension used for cached pages. Defaults to .html.

  • config.action_controller.include_all_helpers configures whether all view helpers are available everywhere or are scoped to the corresponding controller. If set to false, UsersHelper methods are only available for views rendered as part of UsersController. If true, UsersHelper methods are available everywhere. The default configuration behavior (when this option is not explicitly set to true or false) is that all view helpers are available to each controller.

  • config.action_controller.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action Controller. Set to nil to disable logging.

  • config.action_controller.request_forgery_protection_token sets the token parameter name for RequestForgery. Calling protect_from_forgery sets it to :authenticity_token by default.

  • config.action_controller.allow_forgery_protection enables or disables CSRF protection. By default this is false in test mode and true in all other modes.

  • config.action_controller.forgery_protection_origin_check configures whether the HTTP Origin header should be checked against the site's origin as an additional CSRF defense.

  • config.action_controller.per_form_csrf_tokens configures whether CSRF tokens are only valid for the method/action they were generated for.

  • config.action_controller.default_protect_from_forgery determines whether forgery protection is added on ActionController:Base. This is false by default.

  • config.action_controller.relative_url_root can be used to tell Rails that you are deploying to a subdirectory. The default is ENV['RAILS_RELATIVE_URL_ROOT'].

  • config.action_controller.permit_all_parameters sets all the parameters for mass assignment to be permitted by default. The default value is false.

  • config.action_controller.action_on_unpermitted_parameters enables logging or raising an exception if parameters that are not explicitly permitted are found. Set to :log or :raise to enable. The default value is :log in development and test environments, and false in all other environments.

  • config.action_controller.always_permitted_parameters sets a list of permitted parameters that are permitted by default. The default values are ['controller', 'action'].

  • config.action_controller.enable_fragment_cache_logging determines whether to log fragment cache reads and writes in verbose format as follows:

    Read fragment views/v1/2914079/v1/2914079/recordings/70182313-20160225015037000000/d0bdf2974e1ef6d31685c3b392ad0b74 (0.6ms)
    Rendered messages/_message.html.erb in 1.2 ms [cache hit]
    Write fragment views/v1/2914079/v1/2914079/recordings/70182313-20160225015037000000/3b4e249ac9d168c617e32e84b99218b5 (1.1ms)
    Rendered recordings/threads/_thread.html.erb in 1.5 ms [cache miss]
    
    

By default it is set to false which results in following output:

```
Rendered messages/_message.html.erb in 1.2 ms [cache hit]
Rendered recordings/threads/_thread.html.erb in 1.5 ms [cache miss]
```

3.9 Configuring Action Dispatch

  • config.action_dispatch.session_store sets the name of the store for session data. The default is :cookie_store; other valid options include :active_record_store, :mem_cache_store or the name of your own custom class.

  • config.action_dispatch.default_headers is a hash with HTTP headers that are set by default in each response. By default, this is defined as:

    config.action_dispatch.default_headers = {
      'X-Frame-Options' => 'SAMEORIGIN',
      'X-XSS-Protection' => '1; mode=block',
      'X-Content-Type-Options' => 'nosniff',
      'X-Download-Options' => 'noopen',
      'X-Permitted-Cross-Domain-Policies' => 'none',
      'Referrer-Policy' => 'strict-origin-when-cross-origin'
    }
    
    
  • config.action_dispatch.default_charset specifies the default character set for all renders. Defaults to nil.

  • config.action_dispatch.tld_length sets the TLD (top-level domain) length for the application. Defaults to 1.

  • config.action_dispatch.ignore_accept_header is used to determine whether to ignore accept headers from a request. Defaults to false.

  • config.action_dispatch.x_sendfile_header specifies server specific X-Sendfile header. This is useful for accelerated file sending from server. For example it can be set to 'X-Sendfile' for Apache.

  • config.action_dispatch.http_auth_salt sets the HTTP Auth salt value. Defaults to 'http authentication'.

  • config.action_dispatch.signed_cookie_salt sets the signed cookies salt value. Defaults to 'signed cookie'.

  • config.action_dispatch.encrypted_cookie_salt sets the encrypted cookies salt value. Defaults to 'encrypted cookie'.

  • config.action_dispatch.encrypted_signed_cookie_salt sets the signed encrypted cookies salt value. Defaults to 'signed encrypted cookie'.

  • config.action_dispatch.authenticated_encrypted_cookie_salt sets the authenticated encrypted cookie salt. Defaults to 'authenticated encrypted cookie'.

  • config.action_dispatch.encrypted_cookie_cipher sets the cipher to be used for encrypted cookies. This defaults to "aes-256-gcm".

  • config.action_dispatch.signed_cookie_digest sets the digest to be used for signed cookies. This defaults to "SHA1".

  • config.action_dispatch.cookies_rotations allows rotating secrets, ciphers, and digests for encrypted and signed cookies.

  • config.action_dispatch.use_authenticated_cookie_encryption controls whether signed and encrypted cookies use the AES-256-GCM cipher or the older AES-256-CBC cipher. It defaults to true.

  • config.action_dispatch.use_cookies_with_metadata enables writing cookies with the purpose and expiry metadata embedded. It defaults to true.

  • config.action_dispatch.perform_deep_munge configures whether deep_munge method should be performed on the parameters. See Security Guide for more information. It defaults to true.

  • config.action_dispatch.rescue_responses configures what exceptions are assigned to an HTTP status. It accepts a hash and you can specify pairs of exception/status. By default, this is defined as:

  config.action_dispatch.rescue_responses = {
    'ActionController::RoutingError'               => :not_found,
    'AbstractController::ActionNotFound'           => :not_found,
    'ActionController::MethodNotAllowed'           => :method_not_allowed,
    'ActionController::UnknownHttpMethod'          => :method_not_allowed,
    'ActionController::NotImplemented'             => :not_implemented,
    'ActionController::UnknownFormat'              => :not_acceptable,
    'ActionController::InvalidAuthenticityToken'   => :unprocessable_entity,
    'ActionController::InvalidCrossOriginRequest'  => :unprocessable_entity,
    'ActionDispatch::Http::Parameters::ParseError' => :bad_request,
    'ActionController::BadRequest'                 => :bad_request,
    'ActionController::ParameterMissing'           => :bad_request,
    'Rack::QueryParser::ParameterTypeError'        => :bad_request,
    'Rack::QueryParser::InvalidParameterError'     => :bad_request,
    'ActiveRecord::RecordNotFound'                 => :not_found,
    'ActiveRecord::StaleObjectError'               => :conflict,
    'ActiveRecord::RecordInvalid'                  => :unprocessable_entity,
    'ActiveRecord::RecordNotSaved'                 => :unprocessable_entity
  }

Any exceptions that are not configured will be mapped to 500 Internal Server Error.

  • config.action_dispatch.return_only_media_type_on_content_type change the return value of ActionDispatch::Response#content_type to the Content-Type header without modification. Defaults to false.

  • ActionDispatch::Callbacks.before takes a block of code to run before the request.

  • ActionDispatch::Callbacks.after takes a block of code to run after the request.

3.10 Configuring Action View

config.action_view includes a small number of configuration settings:

  • config.action_view.cache_template_loading controls whether or not templates should be reloaded on each request. Defaults to whatever is set for config.cache_classes.

  • config.action_view.field_error_proc provides an HTML generator for displaying errors that come from Active Model. The default is

    Proc.new do |html_tag, instance|
      %Q(<div class="field_with_errors">#{html_tag}</div>).html_safe
    end
    
    
  • config.action_view.default_form_builder tells Rails which form builder to use by default. The default is ActionView::Helpers::FormBuilder. If you want your form builder class to be loaded after initialization (so it's reloaded on each request in development), you can pass it as a String.

  • config.action_view.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action View. Set to nil to disable logging.

  • config.action_view.erb_trim_mode gives the trim mode to be used by ERB. It defaults to '-', which turns on trimming of tail spaces and newline when using <%= -%> or <%= =%>. See the Erubis documentation for more information.

  • config.action_view.embed_authenticity_token_in_remote_forms allows you to set the default behavior for authenticity_token in forms with remote: true. By default it's set to false, which means that remote forms will not include authenticity_token, which is helpful when you're fragment-caching the form. Remote forms get the authenticity from the meta tag, so embedding is unnecessary unless you support browsers without JavaScript. In such case you can either pass authenticity_token: true as a form option or set this config setting to true.

  • config.action_view.prefix_partial_path_with_controller_namespace determines whether or not partials are looked up from a subdirectory in templates rendered from namespaced controllers. For example, consider a controller named Admin::ArticlesController which renders this template:

    <%= render @article %>
    
    

    The default setting is true, which uses the partial at /admin/articles/_article.erb. Setting the value to false would render /articles/_article.erb, which is the same behavior as rendering from a non-namespaced controller such as ArticlesController.

  • config.action_view.raise_on_missing_translations determines whether an error should be raised for missing translations. This defaults to false.

  • config.action_view.automatically_disable_submit_tag determines whether submit_tag should automatically disable on click, this defaults to true.

  • config.action_view.debug_missing_translation determines whether to wrap the missing translations key in a <span> tag or not. This defaults to true.

  • config.action_view.form_with_generates_remote_forms determines whether form_with generates remote forms or not. This defaults to true.

  • config.action_view.form_with_generates_ids determines whether form_with generates ids on inputs. This defaults to false.

  • config.action_view.default_enforce_utf8 determines whether forms are generated with a hidden tag that forces older versions of Internet Explorer to submit forms encoded in UTF-8. This defaults to false.

3.11 Configuring Action Mailbox

config.action_mailbox provides the following configuration options:

  • config.action_mailbox.logger contains the logger used by Action Mailbox. It accepts a logger conforming to the interface of Log4r or the default Ruby Logger class. The default is Rails.logger.
  config.action_mailbox.logger = ActiveSupport::Logger.new(STDOUT)

  • config.action_mailbox.incinerate_after accepts an ActiveSupport::Duration indicating how long after processing ActionMailbox::InboundEmail records should be destroyed. It defaults to 30.days.
   # Incinerate inbound emails 14 days after processing.
   config.action_mailbox.incinerate_after = 14.days

  • config.action_mailbox.queues.incineration accepts a symbol indicating the Active Job queue to use for incineration jobs. It defaults to :action_mailbox_incineration.

  • config.action_mailbox.queues.routing accepts a symbol indicating the Active Job queue to use for routing jobs. It defaults to :action_mailbox_routing.

3.12 Configuring Action Mailer

There are a number of settings available on config.action_mailer:

  • config.action_mailer.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action Mailer. Set to nil to disable logging.

  • config.action_mailer.smtp_settings allows detailed configuration for the :smtp delivery method. It accepts a hash of options, which can include any of these options:

    • :address - Allows you to use a remote mail server. Just change it from its default "localhost" setting.
    • :port - On the off chance that your mail server doesn't run on port 25, you can change it.
    • :domain - If you need to specify a HELO domain, you can do it here.
    • :user_name - If your mail server requires authentication, set the username in this setting.
    • :password - If your mail server requires authentication, set the password in this setting.
    • :authentication - If your mail server requires authentication, you need to specify the authentication type here. This is a symbol and one of :plain, :login, :cram_md5.
    • :enable_starttls_auto - Detects if STARTTLS is enabled in your SMTP server and starts to use it. It defaults to true.
    • :openssl_verify_mode - When using TLS, you can set how OpenSSL checks the certificate. This is useful if you need to validate a self-signed and/or a wildcard certificate. This can be one of the OpenSSL verify constants, :none or :peer -- or the constant directly OpenSSL::SSL::VERIFY_NONE or OpenSSL::SSL::VERIFY_PEER, respectively.
    • :ssl/:tls - Enables the SMTP connection to use SMTP/TLS (SMTPS: SMTP over direct TLS connection).
  • config.action_mailer.sendmail_settings allows detailed configuration for the sendmail delivery method. It accepts a hash of options, which can include any of these options:

    • :location - The location of the sendmail executable. Defaults to /usr/sbin/sendmail.
    • :arguments - The command line arguments. Defaults to -i.
  • config.action_mailer.raise_delivery_errors specifies whether to raise an error if email delivery cannot be completed. It defaults to true.

  • config.action_mailer.delivery_method defines the delivery method and defaults to :smtp. See the configuration section in the Action Mailer guide for more info.

  • config.action_mailer.perform_deliveries specifies whether mail will actually be delivered and is true by default. It can be convenient to set it to false for testing.

  • config.action_mailer.default_options configures Action Mailer defaults. Use to set options like from or reply_to for every mailer. These default to:

    mime_version:  "1.0",
    charset:       "UTF-8",
    content_type: "text/plain",
    parts_order:  ["text/plain", "text/enriched", "text/html"]
    
    

    Assign a hash to set additional options:

    config.action_mailer.default_options = {
      from: "[email protected]"
    }
    
    
  • config.action_mailer.observers registers observers which will be notified when mail is delivered.

    config.action_mailer.observers = ["MailObserver"]
    
    
  • config.action_mailer.interceptors registers interceptors which will be called before mail is sent.

    config.action_mailer.interceptors = ["MailInterceptor"]
    
    
  • config.action_mailer.preview_interceptors registers interceptors which will be called before mail is previewed.

    config.action_mailer.preview_interceptors = ["MyPreviewMailInterceptor"]
    
    
  • config.action_mailer.preview_path specifies the location of mailer previews.

    config.action_mailer.preview_path = "#{Rails.root}/lib/mailer_previews"
    
    
  • config.action_mailer.show_previews enable or disable mailer previews. By default this is true in development.

    config.action_mailer.show_previews = false
    
    
  • config.action_mailer.deliver_later_queue_name specifies the queue name for mailers. By default this is mailers.

  • config.action_mailer.perform_caching specifies whether the mailer templates should perform fragment caching or not. If it's not specified, the default will be true.

  • config.action_mailer.delivery_job specifies delivery job for mail. Defaults to ActionMailer::DeliveryJob.

3.13 Configuring Active Support

There are a few configuration options available in Active Support:

  • config.active_support.bare enables or disables the loading of active_support/all when booting Rails. Defaults to nil, which means active_support/all is loaded.

  • config.active_support.test_order sets the order in which the test cases are executed. Possible values are :random and :sorted. Defaults to :random.

  • config.active_support.escape_html_entities_in_json enables or disables the escaping of HTML entities in JSON serialization. Defaults to true.

  • config.active_support.use_standard_json_time_format enables or disables serializing dates to ISO 8601 format. Defaults to true.

  • config.active_support.time_precision sets the precision of JSON encoded time values. Defaults to 3.

  • config.active_support.use_sha1_digests specifies whether to use SHA-1 instead of MD5 to generate non-sensitive digests, such as the ETag header. Defaults to false.

  • config.active_support.use_authenticated_message_encryption specifies whether to use AES-256-GCM authenticated encryption as the default cipher for encrypting messages instead of AES-256-CBC. This is false by default.

  • ActiveSupport::Logger.silencer is set to false to disable the ability to silence logging in a block. The default is true.

  • ActiveSupport::Cache::Store.logger specifies the logger to use within cache store operations.

  • ActiveSupport::Deprecation.behavior alternative setter to config.active_support.deprecation which configures the behavior of deprecation warnings for Rails.

  • ActiveSupport::Deprecation.silence takes a block in which all deprecation warnings are silenced.

  • ActiveSupport::Deprecation.silenced sets whether or not to display deprecation warnings. The default is false.

3.14 Configuring Active Job

config.active_job provides the following configuration options:

  • config.active_job.queue_adapter sets the adapter for the queuing backend. The default adapter is :async. For an up-to-date list of built-in adapters see the ActiveJob::QueueAdapters API documentation.

    # Be sure to have the adapter's gem in your Gemfile
    # and follow the adapter's specific installation
    # and deployment instructions.
    config.active_job.queue_adapter = :sidekiq
    
    
  • config.active_job.default_queue_name can be used to change the default queue name. By default this is "default".

    config.active_job.default_queue_name = :medium_priority
    
    
  • config.active_job.queue_name_prefix allows you to set an optional, non-blank, queue name prefix for all jobs. By default it is blank and not used.

    The following configuration would queue the given job on the production_high_priority queue when run in production:

    config.active_job.queue_name_prefix = Rails.env
    
    
    class GuestsCleanupJob < ActiveJob::Base
      queue_as :high_priority
      #....
    end
    
    
  • config.active_job.queue_name_delimiter has a default value of '_'. If queue_name_prefix is set, then queue_name_delimiter joins the prefix and the non-prefixed queue name.

    The following configuration would queue the provided job on the video_server.low_priority queue:

    # prefix must be set for delimiter to be used
    config.active_job.queue_name_prefix = 'video_server'
    config.active_job.queue_name_delimiter = '.'
    
    
    class EncoderJob < ActiveJob::Base
      queue_as :low_priority
      #....
    end
    
    
  • config.active_job.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Active Job. You can retrieve this logger by calling logger on either an Active Job class or an Active Job instance. Set to nil to disable logging.

  • config.active_job.custom_serializers allows to set custom argument serializers. Defaults to [].

  • config.active_job.return_false_on_aborted_enqueue change the return value of #enqueue to false instead of the job instance when the enqueuing is aborted. Defaults to false.

3.15 Configuring Action Cable

  • config.action_cable.url accepts a string for the URL for where you are hosting your Action Cable server. You would use this option if you are running Action Cable servers that are separated from your main application.
  • config.action_cable.mount_path accepts a string for where to mount Action Cable, as part of the main server process. Defaults to /cable. You can set this as nil to not mount Action Cable as part of your normal Rails server.

You can find more detailed configuration options in the Action Cable Overview.

3.16 Configuring Active Storage

config.active_storage provides the following configuration options:

  • config.active_storage.variant_processor accepts a symbol :mini_magick or :vips, specifying whether variant transformations will be performed with MiniMagick or ruby-vips. The default is :mini_magick.

  • config.active_storage.analyzers accepts an array of classes indicating the analyzers available for Active Storage blobs. The default is [ActiveStorage::Analyzer::ImageAnalyzer, ActiveStorage::Analyzer::VideoAnalyzer]. The former can extract width and height of an image blob; the latter can extract width, height, duration, angle, and aspect ratio of a video blob.

  • config.active_storage.previewers accepts an array of classes indicating the image previewers available in Active Storage blobs. The default is [ActiveStorage::Previewer::PDFPreviewer, ActiveStorage::Previewer::VideoPreviewer]. The former can generate a thumbnail from the first page of a PDF blob; the latter from the relevant frame of a video blob.

  • config.active_storage.paths accepts a hash of options indicating the locations of previewer/analyzer commands. The default is {}, meaning the commands will be looked for in the default path. Can include any of these options:

    • :ffprobe - The location of the ffprobe executable.
    • :mutool - The location of the mutool executable.
    • :ffmpeg - The location of the ffmpeg executable.
   config.active_storage.paths[:ffprobe] = '/usr/local/bin/ffprobe'

  • config.active_storage.variable_content_types accepts an array of strings indicating the content types that Active Storage can transform through ImageMagick. The default is %w(image/png image/gif image/jpg image/jpeg image/pjpeg image/tiff image/vnd.adobe.photoshop image/vnd.microsoft.icon).

  • config.active_storage.content_types_to_serve_as_binary accepts an array of strings indicating the content types that Active Storage will always serve as an attachment, rather than inline. The default is %w(text/html text/javascript image/svg+xml application/postscript application/x-shockwave-flash text/xml application/xml application/xhtml+xml).

  • config.active_storage.queues.analysis accepts a symbol indicating the Active Job queue to use for analysis jobs. When this option is nil, analysis jobs are sent to the default Active Job queue (see config.active_job.default_queue_name).

   config.active_storage.queues.analysis = :low_priority

  • config.active_storage.queues.purge accepts a symbol indicating the Active Job queue to use for purge jobs. When this option is nil, purge jobs are sent to the default Active Job queue (see config.active_job.default_queue_name).
  config.active_storage.queues.purge = :low_priority

  • config.active_storage.logger can be used to set the logger used by Active Storage. Accepts a logger conforming to the interface of Log4r or the default Ruby Logger class.
  config.active_storage.logger = ActiveSupport::Logger.new(STDOUT)

  • config.active_storage.service_urls_expire_in determines the default expiry of URLs generated by:
    • ActiveStorage::Blob#service_url
    • ActiveStorage::Blob#service_url_for_direct_upload
    • ActiveStorage::Variant#service_url

The default is 5 minutes.

  • config.active_storage.routes_prefix can be used to set the route prefix for the routes served by Active Storage. Accepts a string that will be prepended to the generated routes.
  config.active_storage.routes_prefix = '/files'

The default is /rails/active_storage.

  • config.active_storage.replace_on_assign_to_many determines whether assigning to a collection of attachments declared with has_many_attached replaces any existing attachments or appends to them. The default is true.

  • config.active_storage.draw_routes can be used to toggle Active Storage route generation. The default is true.

3.17 Results of config.load_defaults

config.load_defaults sets new defaults up to and including the version passed. Such that passing, say, '6.0' also gets the new defaults from every version before it.

3.17.1 For '6.0', new defaults from previous versions below and:
  • config.autoloader: :zeitwerk
  • config.action_view.default_enforce_utf8: false
  • config.action_dispatch.use_cookies_with_metadata: true
  • config.action_dispatch.return_only_media_type_on_content_type: false
  • config.action_mailer.delivery_job: "ActionMailer::MailDeliveryJob"
  • config.active_job.return_false_on_aborted_enqueue: true
  • config.active_storage.queues.analysis: :active_storage_analysis
  • config.active_storage.queues.purge: :active_storage_purge
  • config.active_storage.replace_on_assign_to_many: true
  • config.active_record.collection_cache_versioning: true
3.17.2 For '5.2', new defaults from previous versions below and:
  • config.active_record.cache_versioning: true
  • config.action_dispatch.use_authenticated_cookie_encryption: true
  • config.active_support.use_authenticated_message_encryption: true
  • config.active_support.use_sha1_digests: true
  • config.action_controller.default_protect_from_forgery: true
  • config.action_view.form_with_generates_ids: true
3.17.3 For '5.1', new defaults from previous versions below and:
  • config.assets.unknown_asset_fallback: false
  • config.action_view.form_with_generates_remote_forms: true
3.17.4 For '5.0':
  • config.action_controller.per_form_csrf_tokens: true
  • config.action_controller.forgery_protection_origin_check: true
  • ActiveSupport.to_time_preserves_timezone: true
  • config.active_record.belongs_to_required_by_default: true
  • config.ssl_options: { hsts: { subdomains: true } }

3.18 Configuring a Database

Just about every Rails application will interact with a database. You can connect to the database by setting an environment variable ENV['DATABASE_URL'] or by using a configuration file called config/database.yml.

Using the config/database.yml file you can specify all the information needed to access your database:

development:
  adapter: postgresql
  database: blog_development
  pool: 5

This will connect to the database named blog_development using the postgresql adapter. This same information can be stored in a URL and provided via an environment variable like this:

> puts ENV['DATABASE_URL']
postgresql://localhost/blog_development?pool=5

The config/database.yml file contains sections for three different environments in which Rails can run by default:

  • The development environment is used on your development/local computer as you interact manually with the application.
  • The test environment is used when running automated tests.
  • The production environment is used when you deploy your application for the world to use.

If you wish, you can manually specify a URL inside of your config/database.yml

development:
  url: postgresql://localhost/blog_development?pool=5

The config/database.yml file can contain ERB tags <%= %>. Anything in the tags will be evaluated as Ruby code. You can use this to pull out data from an environment variable or to perform calculations to generate the needed connection information.

You don't have to update the database configurations manually. If you look at the options of the application generator, you will see that one of the options is named --database. This option allows you to choose an adapter from a list of the most used relational databases. You can even run the generator repeatedly: cd .. && rails new blog --database=mysql. When you confirm the overwriting of the config/database.yml file, your application will be configured for MySQL instead of SQLite. Detailed examples of the common database connections are below.

3.19 Connection Preference

Since there are two ways to configure your connection (using config/database.yml or using an environment variable) it is important to understand how they can interact.

If you have an empty config/database.yml file but your ENV['DATABASE_URL'] is present, then Rails will connect to the database via your environment variable:

$ cat config/database.yml

$ echo $DATABASE_URL
postgresql://localhost/my_database

If you have a config/database.yml but no ENV['DATABASE_URL'] then this file will be used to connect to your database:

$ cat config/database.yml
development:
  adapter: postgresql
  database: my_database
  host: localhost

$ echo $DATABASE_URL

If you have both config/database.yml and ENV['DATABASE_URL'] set then Rails will merge the configuration together. To better understand this we must see some examples.

When duplicate connection information is provided the environment variable will take precedence:

$ cat config/database.yml
development:
  adapter: sqlite3
  database: NOT_my_database
  host: localhost

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ rails runner 'puts ActiveRecord::Base.configurations'
#<ActiveRecord::DatabaseConfigurations:0x00007fd50e209a28>

$ rails runner 'puts ActiveRecord::Base.configurations.inspect'
#<ActiveRecord::DatabaseConfigurations:0x00007fc8eab02880 @configurations=[
  #<ActiveRecord::DatabaseConfigurations::UrlConfig:0x00007fc8eab020b0
    @env_name="development", @spec_name="primary",
    @config={"adapter"=>"postgresql", "database"=>"my_database", "host"=>"localhost"}
    @url="postgresql://localhost/my_database">
  ]

Here the adapter, host, and database match the information in ENV['DATABASE_URL'].

If non-duplicate information is provided you will get all unique values, environment variable still takes precedence in cases of any conflicts.

$ cat config/database.yml
development:
  adapter: sqlite3
  pool: 5

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ rails runner 'puts ActiveRecord::Base.configurations'
#<ActiveRecord::DatabaseConfigurations:0x00007fd50e209a28>

$ rails runner 'puts ActiveRecord::Base.configurations.inspect'
#<ActiveRecord::DatabaseConfigurations:0x00007fc8eab02880 @configurations=[
  #<ActiveRecord::DatabaseConfigurations::UrlConfig:0x00007fc8eab020b0
    @env_name="development", @spec_name="primary",
    @config={"adapter"=>"postgresql", "database"=>"my_database", "host"=>"localhost", "pool"=>5}
    @url="postgresql://localhost/my_database">
  ]

Since pool is not in the ENV['DATABASE_URL'] provided connection information its information is merged in. Since adapter is duplicate, the ENV['DATABASE_URL'] connection information wins.

The only way to explicitly not use the connection information in ENV['DATABASE_URL'] is to specify an explicit URL connection using the "url" sub key:

$ cat config/database.yml
development:
  url: sqlite3:NOT_my_database

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ rails runner 'puts ActiveRecord::Base.configurations'
#<ActiveRecord::DatabaseConfigurations:0x00007fd50e209a28>

$ rails runner 'puts ActiveRecord::Base.configurations.inspect'
#<ActiveRecord::DatabaseConfigurations:0x00007fc8eab02880 @configurations=[
  #<ActiveRecord::DatabaseConfigurations::UrlConfig:0x00007fc8eab020b0
    @env_name="development", @spec_name="primary",
    @config={"adapter"=>"sqlite3", "database"=>"NOT_my_database"}
    @url="sqlite3:NOT_my_database">
  ]

Here the connection information in ENV['DATABASE_URL'] is ignored, note the different adapter and database name.

Since it is possible to embed ERB in your config/database.yml it is best practice to explicitly show you are using the ENV['DATABASE_URL'] to connect to your database. This is especially useful in production since you should not commit secrets like your database password into your source control (such as Git).

$ cat config/database.yml
production:
  url: <%= ENV['DATABASE_URL'] %>

Now the behavior is clear, that we are only using the connection information in ENV['DATABASE_URL'].

3.19.1 Configuring an SQLite3 Database

Rails comes with built-in support for SQLite3, which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using an SQLite database when creating a new project, but you can always change it later.

Here's the section of the default configuration file (config/database.yml) with connection information for the development environment:

development:
  adapter: sqlite3
  database: db/development.sqlite3
  pool: 5
  timeout: 5000

Rails uses an SQLite3 database for data storage by default because it is a zero configuration database that just works. Rails also supports MySQL (including MariaDB) and PostgreSQL "out of the box", and has plugins for many database systems. If you are using a database in a production environment Rails most likely has an adapter for it.

3.19.2 Configuring a MySQL or MariaDB Database

If you choose to use MySQL or MariaDB instead of the shipped SQLite3 database, your config/database.yml will look a little different. Here's the development section:

development:
  adapter: mysql2
  encoding: utf8mb4
  database: blog_development
  pool: 5
  username: root
  password:
  socket: /tmp/mysql.sock

If your development database has a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the development section as appropriate.

If your MySQL version is 5.5 or 5.6 and want to use the utf8mb4 character set by default, please configure your MySQL server to support the longer key prefix by enabling innodb_large_prefix system variable.

Advisory Locks are enabled by default on MySQL and are used to make database migrations concurrent safe. You can disable advisory locks by setting advisory_locks to false:

production:
  adapter: mysql2
  advisory_locks: false

3.19.3 Configuring a PostgreSQL Database

If you choose to use PostgreSQL, your config/database.yml will be customized to use PostgreSQL databases:

development:
  adapter: postgresql
  encoding: unicode
  database: blog_development
  pool: 5

By default Active Record uses database features like prepared statements and advisory locks. You might need to disable those features if you're using an external connection pooler like PgBouncer:

production:
  adapter: postgresql
  prepared_statements: false
  advisory_locks: false

If enabled, Active Record will create up to 1000 prepared statements per database connection by default. To modify this behavior you can set statement_limit to a different value:

production:
  adapter: postgresql
  statement_limit: 200

The more prepared statements in use: the more memory your database will require. If your PostgreSQL database is hitting memory limits, try lowering statement_limit or disabling prepared statements.

3.19.4 Configuring an SQLite3 Database for JRuby Platform

If you choose to use SQLite3 and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
  adapter: jdbcsqlite3
  database: db/development.sqlite3

3.19.5 Configuring a MySQL or MariaDB Database for JRuby Platform

If you choose to use MySQL or MariaDB and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
  adapter: jdbcmysql
  database: blog_development
  username: root
  password:

3.19.6 Configuring a PostgreSQL Database for JRuby Platform

If you choose to use PostgreSQL and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
  adapter: jdbcpostgresql
  encoding: unicode
  database: blog_development
  username: blog
  password:

Change the username and password in the development section as appropriate.

3.20 Creating Rails Environments

By default Rails ships with three environments: "development", "test", and "production". While these are sufficient for most use cases, there are circumstances when you want more environments.

Imagine you have a server which mirrors the production environment but is only used for testing. Such a server is commonly called a "staging server". To define an environment called "staging" for this server, just create a file called config/environments/staging.rb. Please use the contents of any existing file in config/environments as a starting point and make the necessary changes from there.

That environment is no different than the default ones, start a server with rails server -e staging, a console with rails console -e staging, Rails.env.staging? works, etc.

3.21 Deploy to a subdirectory (relative URL root)

By default Rails expects that your application is running at the root (eg. /). This section explains how to run your application inside a directory.

Let's assume we want to deploy our application to "/app1". Rails needs to know this directory to generate the appropriate routes:

config.relative_url_root = "/app1"

alternatively you can set the RAILS_RELATIVE_URL_ROOT environment variable.

Rails will now prepend "/app1" when generating links.

3.21.1 Using Passenger

Passenger makes it easy to run your application in a subdirectory. You can find the relevant configuration in the Passenger manual.

3.21.2 Using a Reverse Proxy

Deploying your application using a reverse proxy has definite advantages over traditional deploys. They allow you to have more control over your server by layering the components required by your application.

Many modern web servers can be used as a proxy server to balance third-party elements such as caching servers or application servers.

One such application server you can use is Unicorn to run behind a reverse proxy.

In this case, you would need to configure the proxy server (NGINX, Apache, etc) to accept connections from your application server (Unicorn). By default Unicorn will listen for TCP connections on port 8080, but you can change the port or configure it to use sockets instead.

You can find more information in the Unicorn readme and understand the philosophy behind it.

Once you've configured the application server, you must proxy requests to it by configuring your web server appropriately. For example your NGINX config may include:

upstream application_server {
  server 0.0.0.0:8080;
}

server {
  listen 80;
  server_name localhost;

  root /root/path/to/your_app/public;

  try_files $uri/index.html $uri.html @app;

  location @app {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;
    proxy_pass http://application_server;
  }

  # some other configuration
}

Be sure to read the NGINX documentation for the most up-to-date information.

4 Rails Environment Settings

Some parts of Rails can also be configured externally by supplying environment variables. The following environment variables are recognized by various parts of Rails:

  • ENV["RAILS_ENV"] defines the Rails environment (production, development, test, and so on) that Rails will run under.

  • ENV["RAILS_RELATIVE_URL_ROOT"] is used by the routing code to recognize URLs when you deploy your application to a subdirectory.

  • ENV["RAILS_CACHE_ID"] and ENV["RAILS_APP_VERSION"] are used to generate expanded cache keys in Rails' caching code. This allows you to have multiple separate caches from the same application.

5 Using Initializer Files

After loading the framework and any gems in your application, Rails turns to loading initializers. An initializer is any Ruby file stored under config/initializers in your application. You can use initializers to hold configuration settings that should be made after all of the frameworks and gems are loaded, such as options to configure settings for these parts.

There is no guarantee that your initializers will run after all the gem initializers, so any initialization code that depends on a given gem having been initialized should go into a config.after_initialize block.

You can use subfolders to organize your initializers if you like, because Rails will look into the whole file hierarchy from the initializers folder on down.

While Rails supports numbering of initializer file names for load ordering purposes, a better technique is to place any code that need to load in a specific order within the same file. This reduces file name churn, makes dependencies more explicit, and can help surface new concepts within your application.

6 Initialization events

Rails has 5 initialization events which can be hooked into (listed in the order that they are run):

  • before_configuration: This is run as soon as the application constant inherits from Rails::Application. The config calls are evaluated before this happens.

  • before_initialize: This is run directly before the initialization process of the application occurs with the :bootstrap_hook initializer near the beginning of the Rails initialization process.

  • to_prepare: Run after the initializers are run for all Railties (including the application itself), but before eager loading and the middleware stack is built. More importantly, will run upon every request in development, but only once (during boot-up) in production and test.

  • before_eager_load: This is run directly before eager loading occurs, which is the default behavior for the production environment and not for the development environment.

  • after_initialize: Run directly after the initialization of the application, after the application initializers in config/initializers are run.

To define an event for these hooks, use the block syntax within a Rails::Application, Rails::Railtie or Rails::Engine subclass:

module YourApp
  class Application < Rails::Application
    config.before_initialize do
      # initialization code goes here
    end
  end
end

Alternatively, you can also do it through the config method on the Rails.application object:

Rails.application.config.before_initialize do
  # initialization code goes here
end

Some parts of your application, notably routing, are not yet set up at the point where the after_initialize block is called.

6.1 Rails::Railtie#initializer

Rails has several initializers that run on startup that are all defined by using the initializer method from Rails::Railtie. Here's an example of the set_helpers_path initializer from Action Controller:

initializer "action_controller.set_helpers_path" do |app|
  ActionController::Helpers.helpers_path = app.helpers_paths
end

The initializer method takes three arguments with the first being the name for the initializer and the second being an options hash (not shown here) and the third being a block. The :before key in the options hash can be specified to specify which initializer this new initializer must run before, and the :after key will specify which initializer to run this initializer after.

Initializers defined using the initializer method will be run in the order they are defined in, with the exception of ones that use the :before or :after methods.

You may put your initializer before or after any other initializer in the chain, as long as it is logical. Say you have 4 initializers called "one" through "four" (defined in that order) and you define "four" to go before "four" but after "three", that just isn't logical and Rails will not be able to determine your initializer order.

The block argument of the initializer method is the instance of the application itself, and so we can access the configuration on it by using the config method as done in the example.

Because Rails::Application inherits from Rails::Railtie (indirectly), you can use the initializer method in config/application.rb to define initializers for the application.

6.2 Initializers

Below is a comprehensive list of all the initializers found in Rails in the order that they are defined (and therefore run in, unless otherwise stated).

  • load_environment_hook: Serves as a placeholder so that :load_environment_config can be defined to run before it.

  • load_active_support: Requires active_support/dependencies which sets up the basis for Active Support. Optionally requires active_support/all if config.active_support.bare is un-truthful, which is the default.

  • initialize_logger: Initializes the logger (an ActiveSupport::Logger object) for the application and makes it accessible at Rails.logger, provided that no initializer inserted before this point has defined Rails.logger.

  • initialize_cache: If Rails.cache isn't set yet, initializes the cache by referencing the value in config.cache_store and stores the outcome as Rails.cache. If this object responds to the middleware method, its middleware is inserted before Rack::Runtime in the middleware stack.

  • set_clear_dependencies_hook: This initializer - which runs only if cache_classes is set to false - uses ActionDispatch::Callbacks.after to remove the constants which have been referenced during the request from the object space so that they will be reloaded during the following request.

  • initialize_dependency_mechanism: If config.cache_classes is true, configures ActiveSupport::Dependencies.mechanism to require dependencies rather than load them.

  • bootstrap_hook: Runs all configured before_initialize blocks.

  • i18n.callbacks: In the development environment, sets up a to_prepare callback which will call I18n.reload! if any of the locales have changed since the last request. In production mode this callback will only run on the first request.

  • active_support.deprecation_behavior: Sets up deprecation reporting for environments, defaulting to :log for development, :notify for production, and :stderr for test. If a value isn't set for config.active_support.deprecation then this initializer will prompt the user to configure this line in the current environment's config/environments file. Can be set to an array of values.

  • active_support.initialize_time_zone: Sets the default time zone for the application based on the config.time_zone setting, which defaults to "UTC".

  • active_support.initialize_beginning_of_week: Sets the default beginning of week for the application based on config.beginning_of_week setting, which defaults to :monday.

  • active_support.set_configs: Sets up Active Support by using the settings in config.active_support by send'ing the method names as setters to ActiveSupport and passing the values through.

  • action_dispatch.configure: Configures the ActionDispatch::Http::URL.tld_length to be set to the value of config.action_dispatch.tld_length.

  • action_view.set_configs: Sets up Action View by using the settings in config.action_view by send'ing the method names as setters to ActionView::Base and passing the values through.

  • action_controller.assets_config: Initializes the config.actions_controller.assets_dir to the app's public directory if not explicitly configured.

  • action_controller.set_helpers_path: Sets Action Controller's helpers_path to the application's helpers_path.

  • action_controller.parameters_config: Configures strong parameters options for ActionController::Parameters.

  • action_controller.set_configs: Sets up Action Controller by using the settings in config.action_controller by send'ing the method names as setters to ActionController::Base and passing the values through.

  • action_controller.compile_config_methods: Initializes methods for the config settings specified so that they are quicker to access.

  • active_record.initialize_timezone: Sets ActiveRecord::Base.time_zone_aware_attributes to true, as well as setting ActiveRecord::Base.default_timezone to UTC. When attributes are read from the database, they will be converted into the time zone specified by Time.zone.

  • active_record.logger: Sets ActiveRecord::Base.logger - if it's not already set - to Rails.logger.

  • active_record.migration_error: Configures middleware to check for pending migrations.

  • active_record.check_schema_cache_dump: Loads the schema cache dump if configured and available.

  • active_record.warn_on_records_fetched_greater_than: Enables warnings when queries return large numbers of records.

  • active_record.set_configs: Sets up Active Record by using the settings in config.active_record by send'ing the method names as setters to ActiveRecord::Base and passing the values through.

  • active_record.initialize_database: Loads the database configuration (by default) from config/database.yml and establishes a connection for the current environment.

  • active_record.log_runtime: Includes ActiveRecord::Railties::ControllerRuntime which is responsible for reporting the time taken by Active Record calls for the request back to the logger.

  • active_record.set_reloader_hooks: Resets all reloadable connections to the database if config.cache_classes is set to false.

  • active_record.add_watchable_files: Adds schema.rb and structure.sql files to watchable files.

  • active_job.logger: Sets ActiveJob::Base.logger - if it's not already set - to Rails.logger.

  • active_job.set_configs: Sets up Active Job by using the settings in config.active_job by send'ing the method names as setters to ActiveJob::Base and passing the values through.

  • action_mailer.logger: Sets ActionMailer::Base.logger - if it's not already set - to Rails.logger.

  • action_mailer.set_configs: Sets up Action Mailer by using the settings in config.action_mailer by send'ing the method names as setters to ActionMailer::Base and passing the values through.

  • action_mailer.compile_config_methods: Initializes methods for the config settings specified so that they are quicker to access.

  • set_load_path: This initializer runs before bootstrap_hook. Adds paths specified by config.load_paths and all autoload paths to $LOAD_PATH.

  • set_autoload_paths: This initializer runs before bootstrap_hook. Adds all sub-directories of app and paths specified by config.autoload_paths, config.eager_load_paths and config.autoload_once_paths to ActiveSupport::Dependencies.autoload_paths.

  • add_routing_paths: Loads (by default) all config/routes.rb files (in the application and railties, including engines) and sets up the routes for the application.

  • add_locales: Adds the files in config/locales (from the application, railties, and engines) to I18n.load_path, making available the translations in these files.

  • add_view_paths: Adds the directory app/views from the application, railties, and engines to the lookup path for view files for the application.

  • load_environment_config: Loads the config/environments file for the current environment.

  • prepend_helpers_path: Adds the directory app/helpers from the application, railties, and engines to the lookup path for helpers for the application.

  • load_config_initializers: Loads all Ruby files from config/initializers in the application, railties, and engines. The files in this directory can be used to hold configuration settings that should be made after all of the frameworks are loaded.

  • engines_blank_point: Provides a point-in-initialization to hook into if you wish to do anything before engines are loaded. After this point, all railtie and engine initializers are run.

  • add_generator_templates: Finds templates for generators at lib/templates for the application, railties, and engines and adds these to the config.generators.templates setting, which will make the templates available for all generators to reference.

  • ensure_autoload_once_paths_as_subset: Ensures that the config.autoload_once_paths only contains paths from config.autoload_paths. If it contains extra paths, then an exception will be raised.

  • add_to_prepare_blocks: The block for every config.to_prepare call in the application, a railtie, or engine is added to the to_prepare callbacks for Action Dispatch which will be run per request in development, or before the first request in production.

  • add_builtin_route: If the application is running under the development environment then this will append the route for rails/info/properties to the application routes. This route provides the detailed information such as Rails and Ruby version for public/index.html in a default Rails application.

  • build_middleware_stack: Builds the middleware stack for the application, returning an object which has a call method which takes a Rack environment object for the request.

  • eager_load!: If config.eager_load is true, runs the config.before_eager_load hooks and then calls eager_load! which will load all config.eager_load_namespaces.

  • finisher_hook: Provides a hook for after the initialization of process of the application is complete, as well as running all the config.after_initialize blocks for the application, railties, and engines.

  • set_routes_reloader_hook: Configures Action Dispatch to reload the routes file using ActiveSupport::Callbacks.to_run.

  • disable_dependency_loading: Disables the automatic dependency loading if the config.eager_load is set to true.

7 Database pooling

Active Record database connections are managed by ActiveRecord::ConnectionAdapters::ConnectionPool which ensures that a connection pool synchronizes the amount of thread access to a limited number of database connections. This limit defaults to 5 and can be configured in database.yml.

development:
  adapter: sqlite3
  database: db/development.sqlite3
  pool: 5
  timeout: 5000

Since the connection pooling is handled inside of Active Record by default, all application servers (Thin, Puma, Unicorn etc.) should behave the same. The database connection pool is initially empty. As demand for connections increases it will create them until it reaches the connection pool limit.

Any one request will check out a connection the first time it requires access to the database. At the end of the request it will check the connection back in. This means that the additional connection slot will be available again for the next request in the queue.

If you try to use more connections than are available, Active Record will block you and wait for a connection from the pool. If it cannot get a connection, a timeout error similar to that given below will be thrown.

ActiveRecord::ConnectionTimeoutError - could not obtain a database connection within 5.000 seconds (waited 5.000 seconds)

If you get the above error, you might want to increase the size of the connection pool by incrementing the pool option in database.yml

If you are running in a multi-threaded environment, there could be a chance that several threads may be accessing multiple connections simultaneously. So depending on your current request load, you could very well have multiple threads contending for a limited number of connections.

8 Custom configuration

You can configure your own code through the Rails configuration object with custom configuration under either the config.x namespace, or config directly. The key difference between these two is that you should be using config.x if you are defining nested configuration (ex: config.x.nested.hi), and just config for single level configuration (ex: config.hello).

  config.x.payment_processing.schedule = :daily
  config.x.payment_processing.retries  = 3
  config.super_debugger = true

These configuration points are then available through the configuration object:

  Rails.configuration.x.payment_processing.schedule # => :daily
  Rails.configuration.x.payment_processing.retries  # => 3
  Rails.configuration.x.payment_processing.not_set  # => nil
  Rails.configuration.super_debugger                # => true

You can also use Rails::Application.config_for to load whole configuration files:

  # config/payment.yml:
  production:
    environment: production
    merchant_id: production_merchant_id
    public_key:  production_public_key
    private_key: production_private_key
  development:
    environment: sandbox
    merchant_id: development_merchant_id
    public_key:  development_public_key
    private_key: development_private_key

  # config/application.rb
  module MyApp
    class Application < Rails::Application
      config.payment = config_for(:payment)
    end
  end

  Rails.configuration.payment['merchant_id'] # => production_merchant_id or development_merchant_id

9 Search Engines Indexing

Sometimes, you may want to prevent some pages of your application to be visible on search sites like Google, Bing, Yahoo, or Duck Duck Go. The robots that index these sites will first analyze the http://your-site.com/robots.txt file to know which pages it is allowed to index.

Rails creates this file for you inside the /public folder. By default, it allows search engines to index all pages of your application. If you want to block indexing on all pages of your application, use this:

User-agent: *
Disallow: /

To block just specific pages, it's necessary to use a more complex syntax. Learn it on the official documentation.

10 Evented File System Monitor

If the listen gem is loaded Rails uses an evented file system monitor to detect changes when config.cache_classes is false:

group :development do
  gem 'listen', '>= 3.0.5', '< 3.2'
end

Otherwise, in every request Rails walks the application tree to check if anything has changed.

On Linux and macOS no additional gems are needed, but some are required for *BSD and for Windows.

Note that some setups are unsupported.

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