Wordpress Installation on Two Servers - Loadbalancing

If those directories need to be identical, could you put them on another server and mount them remotely via NFS?

There are so so so many ways to improve wordpress performance that don't require a second server and load balancing. In two words: "cache everything".

• Use a php opcode cacher (APC). You can easily achieve 90% cache hit rates with wordpress in under 64MB of mem.

• Enable mysql query cache. You can easily achieve 65% or > cache hit rates with very little mem (site dependent, but never too high).

Most importantly:

Wordpress is a heavy "read" site (vs. write) with most requests limited to a few hundred pages (blog posts). You can increase the requests per second 10 fold by serving static versions of your most popular posts. The best plugin for that is: wp-super-cache. I am not positive if that particular plug-in is compatible with 2k3, but the general idea of automatically creating static versions of your pages and periodically updating them to include new comments, edits, etc is going to be your best bet.

I truly doubt you're site will be doing enough traffic to require two web/app servers if the above common enhancements are implemented(the above can easily handle the slashdot effect). However, two web servers would add a level of fault tolerance. Since performance can be achieved with one web server, then fault tolerance can be achieved using an active/passive setup. This would be simpler and require no sharing of session information.

We ran into the same situation, ended up installing an s3 plugin that hosts your wp uploads directory so you don't have to deal with the syncing.

This is the one we used: http://tantannoodles.com/toolkit/wordpress-s3/

It has been working great so far!