Serve static files from a separate domain

The scaffolding site has at some points had code baked in to serve static files from a separate domain name. This has sometimes led to confusion, and is therefore not always a good thing to have in the scaffolding. This Wiki page instead documents how to accomplish this.

It can be a powerful optimization can be serving static files from a separate domain name. This allows you to use a web server optimized for static files, more easily set expires and cache values, and avoid possibly costly transference of cookies on static files. For more information, please see: http://code.google.com/speed/page-speed/docs/request.html#ServeFromCookielessDomain

All of the work for this goes into the urlRenderOverride method of the Yesod typeclass. A simple implementation would be:

urlRenderOverride master (StaticR s) =
    Just $ uncurry (joinPath master "http://static.example.com") $ renderRoute s
urlRenderOverride _ _ = Nothing