static.domainname.com

Question

I see more and more sites that create vhosts and host files on static.theirdomainname.com. What's up with this? Why is this a pattern I've seen?

Answer 1

Splitting files across multiple domains tricks the browser into opening more pipelines, speeding downloads for clients on broadband connections. Older versions of IE had way too few pipelines by default.

Using a hostname without cookies also reduces the amount of data the client sends the server, slightly speeding things up.

Answer 2

A browser supports only 2 concurrent connections to the same domain. A subdomain or another site will bypass that limit, so many sites create a site for static content to both help with caching and speedup the loading of their site.

Answer 3

Sometimes companies will pay a 3rd party company to host their static content (images, stylesheets, video, etc) on something called a Content Delivery Network (CDN), which has nodes (aka servers) all around the globe. They'll keep copies of your content on all those nodes, so that when people visit your site, the content will be delivered quickly, from the node closest to them. You create a sub-domain (like static.domainname.com) and point it at the CDN's DNS, then they take care of forwarding requests for your static content to the perfect node. Some popular CDNs include Akamai, Amazon CloudFront, and Nirvanix.

Answer 4

With most websites, you use a server which runs your code. In most cases, this is something like Apache. The problem with Apache is that it's very heavy: it uses a lot of resources, it has to load a bunch of stuff that it may or may not end up using, etc. etc.

Effectively, Apache does a lot of beating around the bush before it actually does anything. Granted, if you're running a script, all this beating around the bush may be necessary: loading PHP, initializing settings, etc.

But if the user requests something like, say, and image, you're wasting server resources. Having a separate server with its own subdomain (i.e.: static.xyzcorp.com) lets the programmer offload all of that static file hosting to a server software like lighttpd that FLIES through static files. This server can't run scripts, though (or at least not very complex ones), and really has no other purpose than sitting there and throwing out files.

You might think, "Well, it's only static files. How much could it be?" I've personally had issues where static file hosting on my servers accounted for more than 40% of CPU usage. Offloading the static files to a separate server (or in my case, a CDN) freed up a chunk of bandwidth and a block of CPU time.

Hope this helps!