Is seems that Session Replication in ColdFusion servers less that 9 was considered not something to do on high scale apps. Instead the basic path would be to use round-robin and sticky sessions.
Is this still the case for CF9 or has Session Replication been improved.
I've used session replication on high scale apps with no problem. We have 2-4 instances of ColdFusion on a single server, then multiple physical servers. On top of that, we used sticky sessions to keep sessions on a single instance using round-robin on the load balancers.
If a session died, the session rolled over to another instance on the same physical server and the user was redirected to that instance, unknown to them. If the physical server died, then the load balancer would connect them to another physical server where they would most likely have to login again.
Now, we had some tricks up our sleeves that let us recreate a user session across physical servers too, but that required SiteMinder to manage the overall authentication situation.
The only issue with session replication prior to ColdFusion 9 was that any objects (CFCs) that were stored in session could not be replicated across instances. CF 9 fixed all that.