It really depends what sort of cluster you want. "Cluster" is a very general term. As far as I'm aware, these projects are intended for scientific computing, not web server clusters.
Web server/application clusters are typically not "single system image", instead using a number of machines to appear as a single machine to clients, not the application side.
Such systems typically use a common database, possible utilising database replication or clustering technology.
These things are nontrivial.
Mark