WordPress Nginx proxy cache integrator

Need for Speed?

This plugin handles the wordpress/php side of a statically cached nginx-fronted wordpress (or wordpress mu) site. It makes WordPress emit an “X-Accel-Expires: 0” header when a user is logged in or has taken actions that should cause them to get a customized page on your frontend. This – along with the nginx configuration below – will ensure logged-in users aren’t impacted by your static nginx cache.

Why would you want to statically cache wordpress with nginx?

• INSANE performance. Hardware that could generate 6 pages / second can now generate many thousands.
• Low resource usage. Even on very busy servers, nginx uses only a handful of RAM.
• Unobtrusiveness. You plop nginx in front of wordpress and that’s pretty much it. This plugin (and nginx) is all you need to make your site digg- and slashdot- proof.
• Stability. Nginx is rock solid.
• Faster is better. All the web gurus agree – visitors like faster sites, even when the differences are slight.
• Do more with less. Using a frontend proxy lets you keep your heavy wordpress apaches lightly loaded, letting you handle more concurrent connections and use less RAM.

We’ve been using a caching nginx proxy at the fairly busy blogs.law.harvard.edu since September, 2009. The results have been dramatic: we’ve halved the amount of RAM we need, doubled our outgoing network throughput (nginx is fast!) and have had essentially no significant load spikes.

Drawbacks

There are a few.

• Plugins that rely on php code running on each page view won’t work properly. This is similar to wp-supercache or any of the other static caching plugins. Stats, image rotation, etc. You should implement these features via javascript or third-party services, depending.
• You need to install and configure an nginx frontend proxy – but see the “installation” tab. It’s really not that hard.

Notes

• It is completely harmless to install and activate this plugin before you’ve got the nginx side set up.
• YOU MUST keep this plugin activated as long as you’ve got an nginx frontend proxy active – otherwise, you’ll end up caching too much of your site, and authenticated users won’t see customized pages.
• This plugin helps speed up access for authenticated users mainly because it makes all other traffic a negligible resource drain. I suggest installing apc (or another opcode cache) and – alternatively – a wordpress object cache. Definitely install an opcode cache – leave the object cache for later. You may find you don’t need it!

The Future

This plugin could be set up to allow you to manage caching policies entirely from a wordpress control panel. We’d do this by manipulating the timeout in the “X-Accel-Expires” header based on the type of resource that’s been requested.

It’d be nice to de-cache when pages change via some call from the backend to the nginx frontend.