Here's my tutorial based on my experience with Elastix 2.3 Cluster installation.
I used a HP server as a primary and a PC as Backup.
I'm very sure there should be new "elastix" directories to be included here, probably some other asterisk directories too, but with the current version updated from the last tutorial from Elastix 1.6, pretty much the same directories do the job for excellent mirroring.
It's been working for about a month without problems, so I'm releasing it freely in the hope it can help anyone to understand how to do the cluster. Feedback is greatly appreciated.