nate wrote:
Clustering is a really complex thing to get right, it can often cause more problems than it would otherwise prevent. Even some high end clustering is really poor. A couple of jobs ago I had to use BEA Weblogic application clustering for a massive J2EE app. Ran us roughly $10 or was it $20k per CPU. We had major, major outages with that thing. Most of the time we(and BEA) were able to trace it to the weblogic cluster itself.
So think long and hard about what your trying to accomplish, and if there is another way to get there without relying on clustering. When I say clustering I mean pretty tight integration between the systems in the cluster, where if one box can go whacky it can take the rest of the cluster with it.
Depends on what you are doing, of course, but you can scale a typical web site (lots of viewers of the same content, not too much session-specific data or database writes) by replicating the file content across a bunch of servers and using memcache in front of your database.