SubdomainFu provides a modern implementation of subdomain handling in Rails. It takes aspects from account_location, request_routing, and other snippets found around the web and combines them to provide a single, simple solution for subdomain-based route and url management.

*Note*: SubdomainFu has been rewritten to be compatible with Rails 3. If you are looking to use it on Rails 2.x, please install version v0.5.x instead.


SubdomainFu is available both as a traditional plugin and a GemPlugin. To install it as a traditional plugin:

script/plugin install git://

To use it as a gem, add it to your Gemfile. Until Rails 3 is officially released, the Rails 3 version of the plugin is only available as a prerelease gem:

gem 'subdomain-fu', '1.0.0.beta2'


SubdomainFu works inside of Rails's URL Writing mechanisms to provide an easy and seamless way to link and otherwise understand cross-subdomain routing. You can use the :subdomain option both in named and non-named routes as well as in generated resources routes.

Let's say my domain is ''. Here are some examples of the use of the :subdomain option:

url_for(:controller => "my_controller", 
        :action => "my_action", 
        :subdomain => "awesome") # =>

Now let's say I'm at and I want back to the root. Specifying “false” will remove any current subdomain:

users_url(:subdomain => false)  # =>

Note that this plugin does not honor the :only_path notion of routing when doing so would go against the intent of the command. For example, if I were at again:

users_path(:subdomain => "fun") # =>
users_path(:subdomain => false) # => /users

In this way you can rest assured that you will never misdirect your links to the same subdomain when you meant to change it.

Use in controllers and views

You have access to current_subdomain and current_domain methods.


returns all subdomains. For the URL, it will return “”


returns the domain excluding for the subdomain, including the TLD. For the URL, it will return “”

If what you really want is the entire domain, then use request.domain in your controllers. The purpose of current_domain is to only strip off the first subdomain, if any, and return what's left.


You may need to configure SubdomainFu based on your development setup. To configure SubdomainFu simply call a block in an initializer like so:

SubdomainFu.configure do |config|
  config.option_name = value

Some available options are enumerated below.


A hash for each environment of the size of the top-level domain name. ( = 1, localhost = 0, etc.)

config.tld_size = 1 # sets for current environment
config.tld_sizes = {:development => 0,
                         :test => 0,
                         :production => 1} # set all at once (also the defaults)


Mirrors are the subdomains that are equivalent to no subdomain (i.e. they 'mirror') the usage of the root domain.

config.mirrors = %w(www site we) # Defaults to %w(www)


SubdomainFu also understands the notion of a 'preferred mirror', that is, if you always want your links going to '' instead of '', you can set the preferred mirror like so:

config.preferred_mirror = "www"

Now when you create a link with :subdomain => false in the options the subdomain will default to the preferred mirror.

Routing (Deprecated)

Subdomain constraint routing has been removed from the scope of this plugin as Rails 3 provides the functionality by default. For more info, see this blog post:


Copyright © 2008-2010 Michael Bleigh ( and Intridea, Inc. ( Released under the MIT license