PHP/MySql clusters

I am currently planing a web application and I want to plan it to eventually run on a clust开发者_如何学运维er later.

The cluster would be made of a php web cluster and a mysql cluster and a standalone storage unit (maybe a cluster of it I really don't know how that works :s)

I want to know if the code will be different than when php and mysql are on the same machine and what would be different?

The fact that the web and database servers are on different physical machines wouldn't change your code at all. The only place you'd need to change code is where you connect to the database - replacing the localhost reference with the IP address or hostname of the database server.

A clustered web server may need a different approach for storing sessions. If you got multiple webservers behind a load balancer, consequitive requests from the same session may end up on different servers. You should store the session data in a different place, like a central memcache.

Apart from a few of those issues, you should be fine regarding the web server.

As far as I know, MySQL and clustering are no friends. Although I wasn't really involved in the process, I know there has been a lot of trouble to get two database servers run together in our environment and even now they are not really clustered. They syncronize, but only one is actively used while the other is a fallback server.