Rails 3.0 内置了此功能，您可以从 request.subdomain 访问子域.

Rails 3.0 has this capability built-in, you can access the subdomain from request.subdomain.

您也可以根据子域进行路由:

You can also route based on the subdomain:

class SupportSubdomain
  def self.matches?(request)
    request.subdomain == "support"
  end
end

Basecamp::Application.routes do
  constraints(SupportSubdomain) do
    match "/foo/bar", :to => "foo#bar"
  end
end

如果您使用的是 2.3，则需要使用诸如 subdomain-fu.

If you're using 2.3, you'll need to use a plugin such as subdomain-fu.