random($foo)

You have your clustered web farm and you’re set to go. Except for session handling. You could depend on load balancer for session affinity, you might have some collateral damage (lost sessions) if a machine goes down. You’re probably better off with a separate custom session handler instead (attached to a HA architecture of course):

• PHP4 Session Handler using ADOdb
• Secure MySQL Session Management Handler
• PostgreSQL Session Handler for PHP
• Vulcan Logic SRM
• Msession