Вы можете сделать это с Металлом
./script/generate metal www_redirect
А потом в app / metal / www_redirect.rb
# Allow the metal piece to run in isolation
require(File.dirname(__FILE__) + "/../../config/environment") unless defined?(Rails)
class WwwRedirect
def self.call(env)
if env["SERVER_NAME"] !~ /^www\./
[302, {"Content-Type" => "text/html", "Location" => "http://www.#{env["HTTP_HOST"]}#{env["REQUEST_PATH"]}"}, ["Redirecting..."]]
else
[404, {"Content-Type" => "text/html"}, ["Not Found"]]
end
end
end