Using multiple subdomains on Rails config.action_controller.asset_host

Question

I've setup a CDN using Cloudfront for my Rails 3 app. I created 4 CNAME redirects (cdn1.mywebsite.com, cdn2.mywebasite.com, etc) so I can parallelize the static assets download.

Is it possible to configure rails to use multiple assets hosts?

I tried

config.action_controller.asset_host = ["http://cdn1.mywebasite.com", "http://cdn2.mywebasite.com", "http://cdn3.mywebasite.com", "http://cdn4.mywebasite.com"]

But it didn't work.

Answer 1

See http://api.rubyonrails.org/classes/ActionView/Helpers/AssetUrlHelper.html

Browsers typically open at most two simultaneous connections to a single host, which means your assets often have to wait for other assets to finish downloading. You can alleviate this by using a %d wildcard in the asset_host. For example, “assets%d.example.com”. If that wildcard is present Rails distributes asset requests among the corresponding four hosts “assets0.example.com”, …, “assets3.example.com”. With this trick browsers will open eight simultaneous connections rather than two.

You'd need to tweak your DNS a bit to start counting from 0 and then do:

config.action_controller.asset_host = 'http://cdn%d.mywebasite.com'