load balancer and HA

[Martin Karbon]

Hi!
just wanted to know if anyone knows an opensource solution for a so 
called transparent failover: what I mean with that is, I installed two 
machines with haproxy on it which comunicate with each other via 
heartbeat. If one fails the other one goes from passive to active but 
all sessions are lost and users have to reconnect.
I've seen some costly solutions for load balancing which claim to have 
some sort of shared memory to allow this kind of failover with which 
users do not lose connection, so I was just wondering if someone knows a 
product or has some ideas on how this kind of technology is implementable.
Best regards
Martin