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Configuring Rails Applications
This guide covers the configuration and initialization features available to Rails applications.
After reading this guide, you will know:
- How to adjust the behavior of your Rails applications.
- How to add additional code to be run at application start time.
Locations for Initialization Code
Rails offers four standard spots to place initialization code:
config/application.rb
- Environment-specific configuration files
- Initializers
- After-initializers
Running Code Before Rails
In the rare event that your application needs to run some code before Rails itself is loaded, put it above the call to require 'rails/all'
in config/application.rb
.
Configuring Rails Components
In general, the work of configuring Rails means configuring the components of Rails, as well as configuring Rails itself. The configuration file config/application.rb
and environment-specific configuration files (such as config/environments/production.rb
) allow you to specify the various settings that you want to pass down to all of the components.
For example, the config/application.rb
file includes this setting:
config.autoload_paths += %W(#{config.root}/extras)
This is a setting for Rails itself. If you want to pass settings to individual Rails components, you can do so via the same config
object in config/application.rb
:
config.active_record.schema_format = :ruby
Rails will use that particular setting to configure Active Record.
Rails General Configuration
These configuration methods are to be called on a Rails::Railtie
object, such as a subclass of Rails::Engine
or Rails::Application
.
-
config.after_initialize
takes a block which will be run after Rails has finished initializing the application. That includes the initialization of the framework itself, engines, and all the application's initializers inconfig/initializers
. Note that this block will be run for rake tasks. Useful for configuring values set up by other initializers:config.after_initialize do ActionView::Base.sanitized_allowed_tags.delete 'div' end
-
config.asset_host
sets the host for the assets. Useful when CDNs are used for hosting assets, or when you want to work around the concurrency constraints builtin in browsers using different domain aliases. Shorter version ofconfig.action_controller.asset_host
. -
config.autoload_once_paths
accepts an array of paths from which Rails will autoload constants that won't be wiped per request. Relevant ifconfig.cache_classes
is false, which is the case in development mode by default. Otherwise, all autoloading happens only once. All elements of this array must also be inautoload_paths
. Default is an empty array. -
config.autoload_paths
accepts an array of paths from which Rails will autoload constants. Default is all directories underapp
. -
config.cache_classes
controls whether or not application classes and modules should be reloaded on each request. Defaults to false in development mode, and true in test and production modes. Can also be enabled withthreadsafe!
. -
config.action_view.cache_template_loading
controls whether or not templates should be reloaded on each request. Defaults to whatever is set forconfig.cache_classes
. -
config.beginning_of_week
sets the default beginning of week for the application. Accepts a valid week day symbol (e.g.:monday
). -
config.cache_store
configures which cache store to use for Rails caching. Options include one of the symbols:memory_store
,:file_store
,:mem_cache_store
,:null_store
, or an object that implements the cache API. Defaults to:file_store
if the directorytmp/cache
exists, and to:memory_store
otherwise. -
config.colorize_logging
specifies whether or not to use ANSI color codes when logging information. Defaults to true. -
config.consider_all_requests_local
is a flag. If true then any error will cause detailed debugging information to be dumped in the HTTP response, and theRails::Info
controller will show the application runtime context in/rails/info/properties
. True by default in development and test environments, and false in production mode. For finer-grained control, set this to false and implementlocal_request?
in controllers to specify which requests should provide debugging information on errors. -
config.console
allows you to set class that will be used as console you runrails console
. It's best to run it inconsole
block:console do # this block is called only when running console, # so we can safely require pry here require "pry" config.console = Pry end
-
config.dependency_loading
is a flag that allows you to disable constant autoloading setting it to false. It only has effect ifconfig.cache_classes
is true, which it is by default in production mode. This flag is set to false byconfig.threadsafe!
. -
config.eager_load
when true, eager loads all registeredconfig.eager_load_namespaces
. This includes your application, engines, Rails frameworks and any other registered namespace. -
config.eager_load_namespaces
registers namespaces that are eager loaded whenconfig.eager_load
is true. All namespaces in the list must respond to theeager_load!
method. -
config.eager_load_paths
accepts an array of paths from which Rails will eager load on boot if cache classes is enabled. Defaults to every folder in theapp
directory of the application. -
config.encoding
sets up the application-wide encoding. Defaults to UTF-8. -
config.exceptions_app
sets the exceptions application invoked by the ShowException middleware when an exception happens. Defaults toActionDispatch::PublicExceptions.new(Rails.public_path)
. -
config.file_watcher
the class used to detect file updates in the filesystem whenconfig.reload_classes_only_on_change
is true. Must conform toActiveSupport::FileUpdateChecker
API. -
config.filter_parameters
used for filtering out the parameters that you don't want shown in the logs, such as passwords or credit card numbers. New applications filter out passwords by adding the followingconfig.filter_parameters+=[:password]
inconfig/initializers/filter_parameter_logging.rb
. -
config.force_ssl
forces all requests to be under HTTPS protocol by usingActionDispatch::SSL
middleware. -
config.log_formatter
defines the formatter of the Rails logger. This option defaults to an instance ofActiveSupport::Logger::SimpleFormatter
for all modes except production, where it defaults toLogger::Formatter
. -
config.log_level
defines the verbosity of the Rails logger. This option defaults to:debug
for all modes except production, where it defaults to:info
. -
config.log_tags
accepts a list of methods that respond torequest
object. This makes it easy to tag log lines with debug information like subdomain and request id - both very helpful in debugging multi-user production applications. -
config.logger
accepts a logger conforming to the interface of Log4r or the default RubyLogger
class. Defaults to an instance ofActiveSupport::Logger
, with auto flushing off in production mode. -
config.middleware
allows you to configure the application's middleware. This is covered in depth in the Configuring Middleware section below. -
config.reload_classes_only_on_change
enables or disables reloading of classes only when tracked files change. By default tracks everything on autoload paths and is set to true. Ifconfig.cache_classes
is true, this option is ignored. -
config.secret_key_base
used for specifying a key which allows sessions for the application to be verified against a known secure key to prevent tampering. Applications getconfig.secret_key_base
initialized to a random key inconfig/initializers/secret_token.rb
. -
config.serve_static_assets
configures Rails itself to serve static assets. Defaults to true, but in the production environment is turned off as the server software (e.g. Nginx or Apache) used to run the application should serve static assets instead. Unlike the default setting set this to true when running (absolutely not recommended!) or testing your app in production mode using WEBrick. Otherwise you won't be able use page caching and requests for files that exist regularly under the public directory will anyway hit your Rails app. -
config.session_store
is usually set up inconfig/initializers/session_store.rb
and specifies what class to use to store the session. Possible values are:cookie_store
which is the default,:mem_cache_store
, and:disabled
. The last one tells Rails not to deal with sessions. Custom session stores can also be specified:config.session_store :my_custom_store
This custom store must be defined as
ActionDispatch::Session::MyCustomStore
. -
config.time_zone
sets the default time zone for the application and enables time zone awareness for Active Record.
Configuring Assets
config.assets.enabled
a flag that controls whether the asset pipeline is enabled. It is set to true by default.
config.assets.raise_runtime_errors
Set this flag to true
to enable additional runtime error checking. Recommended in config/environments/development.rb
to minimize unexpected behavior when deploying to production
.
-
config.assets.compress
a flag that enables the compression of compiled assets. It is explicitly set to true inconfig/environments/production.rb
. -
config.assets.css_compressor
defines the CSS compressor to use. It is set by default bysass-rails
. The unique alternative value at the moment is:yui
, which uses theyui-compressor
gem. -
config.assets.js_compressor
defines the JavaScript compressor to use. Possible values are:closure
,:uglifier
and:yui
which require the use of theclosure-compiler
,uglifier
oryui-compressor
gems respectively. -
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 thanapplication.css
andapplication.js
) which are to be precompiled whenrake assets:precompile
is run. -
config.assets.prefix
defines the prefix where assets are served from. Defaults to/assets
. -
config.assets.digest
enables the use of MD5 fingerprints in asset names. Set totrue
by default inproduction.rb
. -
config.assets.debug
disables the concatenation and compression of assets. Set totrue
by default indevelopment.rb
. -
config.assets.cache_store
defines the cache store that Sprockets will use. The default is the Rails file store. -
config.assets.version
is an option string that is used in MD5 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 RubyLogger
class. Defaults to the same configured atconfig.logger
. Settingconfig.assets.logger
to false will turn off served assets logging.
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 totrue
.force_plural
allows pluralized model names. Defaults tofalse
.helper
defines whether or not to generate helpers. Defaults totrue
.integration_tool
defines which integration tool to use. Defaults tonil
.javascripts
turns on the hook for JavaScript files in generators. Used in Rails for when thescaffold
generator is run. Defaults totrue
.javascript_engine
configures the engine to be used (for eg. coffee) when generating assets. Defaults tonil
.orm
defines which orm to use. Defaults tofalse
and will use Active Record by default.resource_controller
defines which generator to use for generating a controller when usingrails generate resource
. Defaults to:controller
.scaffold_controller
different fromresource_controller
, defines which generator to use for generating a scaffolded controller when usingrails generate scaffold
. Defaults to:scaffold_controller
.stylesheets
turns on the hook for stylesheets in generators. Used in Rails for when thescaffold
generator is run, but this hook can be used in other generates as well. Defaults totrue
.stylesheet_engine
configures the stylesheet engine (for eg. sass) to be used when generating assets. Defaults to:css
.test_framework
defines which test framework to use. Defaults tofalse
and will use Test::Unit by default.template_engine
defines which template engine to use, such as ERB or Haml. Defaults to:erb
.
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 under HTTPS protocol. Will be available ifconfig.force_ssl
is set totrue
. Options passed to this can be configured by usingconfig.ssl_options
.ActionDispatch::Static
is used to serve static assets. Disabled ifconfig.serve_static_assets
isfalse
.Rack::Lock
wraps the app in mutex so it can only be called by a single thread at a time. Only enabled whenconfig.cache_classes
isfalse
.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 anX-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 ifconfig.consider_all_requests_local
is set totrue
. Ifconfig.action_dispatch.show_exceptions
is set tofalse
, exceptions will be raised regardless.ActionDispatch::RequestId
makes a unique X-Request-Id header available to the response and enables theActionDispatch::Request#uuid
method.ActionDispatch::RemoteIp
checks for IP spoofing attacks and gets validclient_ip
from request headers. Configurable with theconfig.action_dispatch.ip_spoofing_check
, andconfig.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 withconfig.action_dispatch.x_sendfile_header
.ActionDispatch::Callbacks
runs the prepare callbacks before serving the request.ActiveRecord::ConnectionAdapters::ConnectionManagement
cleans active connections after each request, unless therack.test
key in the request environment is set totrue
.ActiveRecord::QueryCache
caches all SELECT queries generated in a request. If any INSERT or UPDATE takes place then the cache is cleaned.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 theconfig.action_controller.session_store
to an alternate value. Additionally, options passed to this can be configured by usingconfig.action_controller.session_options
.ActionDispatch::Flash
sets up theflash
keys. Only available ifconfig.action_controller.session_store
is set to a value.ActionDispatch::ParamsParser
parses out parameters from the request intoparams
.Rack::MethodOverride
allows the method to be overridden ifparams[:_method]
is set. This is the middleware which supports the PATCH, PUT, and DELETE HTTP method types.ActionDispatch::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 ActionDispatch::Head, Magical::Unicorns
There's also insert_after
which will insert a middleware after another:
config.middleware.insert_after ActionDispatch::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"
Configuring i18n
All these configuration options are delegated to the I18n
library.
-
config.i18n.available_locales
whitelists the 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 theavailable_locales
list, raising anI18n::InvalidLocale
exception when setting an unavailable locale. Defaults totrue
. 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 toconfig/locales/*.{yml,rb}
.
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 callinglogger
on either an Active Record model class or an Active Record model instance. Set tonil
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 namedid
(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 classcustomerid
**:table_name_with_underscore
would make the primary key for the Customer classcustomer_id
-
config.active_record.table_name_prefix
lets you set a global string to be prepended to table names. If you set this tonorthwest_
, then the Customer class will look fornorthwest_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 forcustomers_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.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 thecustomers
table. If set to false, then the Customer class will use thecustomer
table. -
config.active_record.default_timezone
determines whether to useTime.local
(if set to:local
) orTime.utc
(if set to:utc
) when pulling dates and times from the database. The default is:utc
for Rails, although Active Record defaults to:local
when used outside of Rails. -
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.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:number
. -
config.active_record.record_timestamps
is a boolean value which controls whether or not timestamping ofcreate
andupdate
operations on a model occur. The default value istrue
. -
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 lockingconfig.active_record.lock_optimistically
since concurrent updates may write attributes based on a possibly stale read state. The default value istrue
. -
config.active_record.attribute_types_cached_by_default
sets the attribute types thatActiveRecord::AttributeMethods
will cache by default on reads. The default is[:datetime, :timestamp, :time, :date]
. -
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 withdb/schema.rb
(ordb/structure.sql
) when you run your tests. The default is true.
The MySQL adapter adds one additional configuration option:
ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans
controls whether Active Record will consider alltinyint(1)
columns in a MySQL database to be booleans and is true by default.
The schema dumper adds one additional configuration option:
ActiveRecord::SchemaDumper.ignore_tables
accepts an array of tables that should not be included in any generated schema file. This setting is ignored unlessconfig.active_record.schema_format == :ruby
.
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 caching or not. Set to false in development mode, true in production. -
config.action_controller.default_static_extension
configures the extension used for cached pages. Defaults to.html
. -
config.action_controller.default_charset
specifies the default character set for all renders. The default is "utf-8". -
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 tonil
to disable logging. -
config.action_controller.request_forgery_protection_token
sets the token parameter name for RequestForgery. Callingprotect_from_forgery
sets it to:authenticity_token
by default. -
config.action_controller.allow_forgery_protection
enables or disables CSRF protection. By default this isfalse
in test mode andtrue
in all other modes. -
config.action_controller.relative_url_root
can be used to tell Rails that you are deploying to a subdirectory. The default isENV['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 isfalse
. -
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, andfalse
in all other environments.
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' }
-
config.action_dispatch.tld_length
sets the TLD (top-level domain) length for the application. Defaults to1
. -
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'
. -
ActionDispatch::Callbacks.before
takes a block of code to run before the request. -
ActionDispatch::Callbacks.to_prepare
takes a block to run afterActionDispatch::Callbacks.before
, but before the request. Runs for every request indevelopment
mode, but only once forproduction
or environments withcache_classes
set totrue
. -
ActionDispatch::Callbacks.after
takes a block of code to run after the request.
Configuring Action View
config.action_view
includes a small number of configuration settings:
-
config.action_view.field_error_proc
provides an HTML generator for displaying errors that come from Active Record. The default isProc.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 isActionView::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 aString
-
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 tonil
to disable logging. -
config.action_view.erb_trim_mode
gives the trim mode to be used by ERB. It defaults to'-'
. See the ERB documentation for more information. -
config.action_view.embed_authenticity_token_in_remote_forms
allows you to set the default behavior forauthenticity_token
in forms with:remote => true
. By default it's set to false, which means that remote forms will not includeauthenticity_token
, which is helpful when you're fragment-caching the form. Remote forms get the authenticity from themeta
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 totrue
-
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 namedAdmin::PostsController
which renders this template:<%= render @post %>
The default setting is
true
, which uses the partial at/admin/posts/_post.erb
. Setting the value tofalse
would render/posts/_post.erb
, which is the same behavior as rendering from a non-namespaced controller such asPostsController
.
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 tonil
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
.
-
config.action_mailer.sendmail_settings
allows detailed configuration for thesendmail
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 -t
.
-
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 likefrom
orreply_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: "noreply@example.com" }
-
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"]
Configuring Active Support
There are a few configuration options available in Active Support:
-
config.active_support.bare
enables or disables the loading ofactive_support/all
when booting Rails. Defaults tonil
, which meansactive_support/all
is loaded. -
config.active_support.escape_html_entities_in_json
enables or disables the escaping of HTML entities in JSON serialization. Defaults tofalse
. -
config.active_support.use_standard_json_time_format
enables or disables serializing dates to ISO 8601 format. Defaults totrue
. -
config.active_support.time_precision
sets the precision of JSON encoded time values. Defaults to3
. -
ActiveSupport::Logger.silencer
is set tofalse
to disable the ability to silence logging in a block. The default istrue
. -
ActiveSupport::Cache::Store.logger
specifies the logger to use within cache store operations. -
ActiveSupport::Deprecation.behavior
alternative setter toconfig.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. -
ActiveSupport::Logger.silencer
is set tofalse
to disable the ability to silence logging in a block. The default istrue
.
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.
TIP: 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.
Connection Preference
Since there are two ways to set your connection, via environment variable it is important to understand how the two 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.connections'
{"development"=>{"adapter"=>"postgresql", "host"=>"localhost", "database"=>"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.connections'
{"development"=>{"adapter"=>"postgresql", "host"=>"localhost", "database"=>"my_database", "pool"=>5}}
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 connectinon using the "url"
sub key:
$ cat config/database.yml
development:
url: sqlite3://localhost/NOT_my_database
$ echo $DATABASE_URL
postgresql://localhost/my_database
$ rails runner 'puts ActiveRecord::Base.connections'
{"development"=>{"adapter"=>"sqlite3", "host"=>"localhost", "database"=>"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']
.
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
NOTE: Rails uses an SQLite3 database for data storage by default because it is a zero configuration database that just works. Rails also supports MySQL 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.
Configuring a MySQL Database
If you choose to use MySQL instead of the shipped SQLite3 database, your config/database.yml
will look a little different. Here's the development section:
development:
adapter: mysql2
encoding: utf8
database: blog_development
pool: 5
username: root
password:
socket: /tmp/mysql.sock
If your development computer's MySQL installation includes 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.
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
username: blog
password:
Prepared Statements can be disabled thus:
production:
adapter: postgresql
prepared_statements: false
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
Configuring a MySQL Database for JRuby Platform
If you choose to use MySQL 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:
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.
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 staging
, Rails.env.staging?
works, etc.
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.
Using Passenger
Passenger makes it easiy to run your application in a subdirectory. You can find the relevant configuration in the passenger manual.
Using a Reverse Proxy
TODO
Considerations when deploying to a subdirectory
Deploying to a subdirectory in production has implications on various parts of Rails.
- development environment:
- testing environment:
- serving static assets:
- asset pipeline:
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"]
andENV["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.
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.
NOTE: 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.
TIP: If you have any ordering dependency in your initializers, you can control the load order through naming. Initializer files are loaded in alphabetical order by their path. For example, 01_critical.rb
will be loaded before 02_normal.rb
.
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 fromRails::Application
. Theconfig
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 indevelopment
, but only once (during boot-up) inproduction
andtest
. -
before_eager_load
: This is run directly before eager loading occurs, which is the default behavior for theproduction
environment and not for thedevelopment
environment. -
after_initialize
: Run directly after the initialization of the application, after the application initializers inconfig/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
WARNING: Some parts of your application, notably routing, are not yet set up at the point where the after_initialize
block is called.
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.
WARNING: 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.
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
Requiresactive_support/dependencies
which sets up the basis for Active Support. Optionally requiresactive_support/all
ifconfig.active_support.bare
is un-truthful, which is the default. -
initialize_logger
Initializes the logger (anActiveSupport::Logger
object) for the application and makes it accessible atRails.logger
, provided that no initializer inserted before this point has definedRails.logger
. -
initialize_cache
IfRails.cache
isn't set yet, initializes the cache by referencing the value inconfig.cache_store
and stores the outcome asRails.cache
. If this object responds to themiddleware
method, its middleware is inserted beforeRack::Runtime
in the middleware stack. -
set_clear_dependencies_hook
Provides a hook foractive_record.set_dispatch_hooks
to use, which will run before this initializer. This initializer - which runs only ifcache_classes
is set tofalse
- usesActionDispatch::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
Ifconfig.cache_classes
is true, configuresActiveSupport::Dependencies.mechanism
torequire
dependencies rather thanload
them. -
bootstrap_hook
Runs all configuredbefore_initialize
blocks. -
i18n.callbacks
In the development environment, sets up ato_prepare
callback which will callI18n.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 forconfig.active_support.deprecation
then this initializer will prompt the user to configure this line in the current environment'sconfig/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 theconfig.time_zone
setting, which defaults to "UTC". -
active_support.initialize_beginning_of_week
Sets the default beginning of week for the application based onconfig.beginning_of_week
setting, which defaults to:monday
. -
action_dispatch.configure
Configures theActionDispatch::Http::URL.tld_length
to be set to the value ofconfig.action_dispatch.tld_length
. -
action_view.set_configs
Sets up Action View by using the settings inconfig.action_view
bysend
'ing the method names as setters toActionView::Base
and passing the values through. -
action_controller.logger
SetsActionController::Base.logger
- if it's not already set - toRails.logger
. -
action_controller.initialize_framework_caches
SetsActionController::Base.cache_store
- if it's not already set - toRails.cache
. -
action_controller.set_configs
Sets up Action Controller by using the settings inconfig.action_controller
bysend
'ing the method names as setters toActionController::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
SetsActiveRecord::Base.time_zone_aware_attributes
to true, as well as settingActiveRecord::Base.default_timezone
to UTC. When attributes are read from the database, they will be converted into the time zone specified byTime.zone
. -
active_record.logger
SetsActiveRecord::Base.logger
- if it's not already set - toRails.logger
. -
active_record.set_configs
Sets up Active Record by using the settings inconfig.active_record
bysend
'ing the method names as setters toActiveRecord::Base
and passing the values through. -
active_record.initialize_database
Loads the database configuration (by default) fromconfig/database.yml
and establishes a connection for the current environment. -
active_record.log_runtime
IncludesActiveRecord::Railties::ControllerRuntime
which is responsible for reporting the time taken by Active Record calls for the request back to the logger. -
active_record.set_dispatch_hooks
Resets all reloadable connections to the database ifconfig.cache_classes
is set tofalse
. -
action_mailer.logger
SetsActionMailer::Base.logger
- if it's not already set - toRails.logger
. -
action_mailer.set_configs
Sets up Action Mailer by using the settings inconfig.action_mailer
bysend
'ing the method names as setters toActionMailer::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 beforebootstrap_hook
. Adds thevendor
,lib
, all directories ofapp
and any paths specified byconfig.load_paths
to$LOAD_PATH
. -
set_autoload_paths
This initializer runs beforebootstrap_hook
. Adds all sub-directories ofapp
and paths specified byconfig.autoload_paths
toActiveSupport::Dependencies.autoload_paths
. -
add_routing_paths
Loads (by default) allconfig/routes.rb
files (in the application and railties, including engines) and sets up the routes for the application. -
add_locales
Adds the files inconfig/locales
(from the application, railties and engines) toI18n.load_path
, making available the translations in these files. -
add_view_paths
Adds the directoryapp/views
from the application, railties and engines to the lookup path for view files for the application. -
load_environment_config
Loads theconfig/environments
file for the current environment. -
append_asset_paths
Finds asset paths for the application and all attached railties and keeps a track of the available directories inconfig.static_asset_paths
. -
prepend_helpers_path
Adds the directoryapp/helpers
from the application, railties and engines to the lookup path for helpers for the application. -
load_config_initializers
Loads all Ruby files fromconfig/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 atlib/templates
for the application, railties and engines and adds these to theconfig.generators.templates
setting, which will make the templates available for all generators to reference. -
ensure_autoload_once_paths_as_subset
Ensures that theconfig.autoload_once_paths
only contains paths fromconfig.autoload_paths
. If it contains extra paths, then an exception will be raised. -
add_to_prepare_blocks
The block for everyconfig.to_prepare
call in the application, a railtie or engine is added to theto_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 forrails/info/properties
to the application routes. This route provides the detailed information such as Rails and Ruby version forpublic/index.html
in a default Rails application. -
build_middleware_stack
Builds the middleware stack for the application, returning an object which has acall
method which takes a Rack environment object for the request. -
eager_load!
Ifconfig.eager_load
is true, runs theconfig.before_eager_load
hooks and then callseager_load!
which will load allconfig.eager_load_namespaces
. -
finisher_hook
Provides a hook for after the initialization of process of the application is complete, as well as running all theconfig.after_initialize
blocks for the application, railties and engines. -
set_routes_reloader
Configures Action Dispatch to reload the routes file usingActionDispatch::Callbacks.to_prepare
. -
disable_dependency_loading
Disables the automatic dependency loading if theconfig.eager_load
is set to true.
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, mongrel, Unicorn etc.) should behave the same. Initially, the database connection pool is empty and it will create additional connections as the demand for them increases, until it reaches the connection pool limit.
Any one request will check out a connection the first time it requires access to the database, after which it will check the connection back in, at the end of the request, meaning 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 and wait for a connection from the pool. When it cannot get connection, a timeout error similar to given below will be thrown.
ActiveRecord::ConnectionTimeoutError - could not obtain a database connection within 5 seconds. The max pool size is currently 5; consider increasing it:
If you get the above error, you might want to increase the size of connection
pool by incrementing the pool
option in database.yml
NOTE. If you have enabled Rails.threadsafe!
mode then 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 amount of connections.