I'm internationalizing an app, and am splitting the locales by subdomain (es.bustaname.com, fr.bustaname.com, etc...) While other people have solved the page_caching issue with subdomains before, I couldn't find a clear explanation. All of the examples were missing one piece of information.

Controller

Add the following into your controller.

class ApplicationController < ActionController::Base
  # Cache pages with the subdomain
  def cache_page(content = nil, options = nil)
    path = "/#{request.host}/"
    path << case options
    when Hash
      url_for(options.merge(:only_path => true, :skip_relative_url_root => true, :format => params[:format]))
    when String
      options
    else
      if request.path.empty? || request.path == '/'
        '/index'
      else
        request.path
      end
    end
    super(content, path)
  end
end

This will cache each subdomain in its own directory.

To keep things clean I also move my cache directory into public/cache Just add the following to your environment.rb inside of the run block.

Rails::Initializer.run do |config|
	config.action_controller.page_cache_directory = RAILS_ROOT + '/public/cache/'
end

Then the part everyone else seemed to miss is that this will make something like caches_page :index (note the pluralization) work, even though we defined a cache_page method. ActionController::Base has both a class and an instance version of cache_page and a class method called cache_pages. You want to use the class method cache_pages.

Nginx

Next place the following in your nginx.conf file:

# If the file exists in the public folder, send it
if (-f $request_filename) {
  break;
}

# Check / files with index.html
if (-f $document_root/cache/$host/$uri/index.html) {
  rewrite (.*) /cache/$host/$1/index.html break;
}

# Check the path + .html
if (-f $document_root/cache/$host/$uri.html) {
  rewrite (.*) /cache/$host/$1.html break;
}

# Check directly
if (-f $document_root/cache/$host/$uri) {
  rewrite (.*) /cache/$host/$1 break;
}

This will look up cached files in /cache/$host/ and should send the files correctly. Be sure to add the nginx config before you send it to mongrel/thin/etc..