moving ip of one VM to another VM
you can achieve "floating IPs" also known as VIP or virtual IP with either:
- keepalived (VRRP)
- pacemaker/corosync
- carp (http://manpages.ubuntu.com/manpages/precise/man4/carp.4freebsd.html)
FYI: you can also achieve redundancy in the client by letting him choose the healthy server(s) from a list.
note that implementing redundancy between VMs on the same host is not recommended. (the host is the Single Point Of Failure)