Remus
http://dsg.cs.ubc.ca/remus/

Remus provides transparent, comprehensive high availability to ordinary virtual machines running on the Xen virtual machine monitor. It does this by maintaining a completely up-to-date copy of a running VM on a backup server, which automatically activates if the primary server fails.

HA solution for Xen

keepalived --vrrp で、マルチマスターフェイルオーバーする