New on VoidWeb.com there's a post looking at clustering PHP applications with the help of the mod_proxy component that can be added into the Apache web server.

Often for my clients, I have to prepare the deployment strategy for their LAMP based web applications. Some of them are small to medium businesses and are starting up so a single server setup work out for them. But there are few large web applications too which are growing continuously in terms of users and demands scaling either horizontally or vertically.

They give a brief overview of what vertical and horizontal scaling are as well as a simple layout of a basic PHP-based cluster. They list some of the requirements for this simple cluster and how it should all work (in theory) and start in on how to set it all up (practically). In the end you'll have a light proxy setup that will rotate around between the servers but do it transparently from node to node.