IP failover between two servers with Centos

keepalived:
http://tecadmin.net/ip-failover-setup-using-keepalived-on-centos-redhat-6/
http://www.keepalived.org/

ucarp:
http://ragzilla.co.uk/setup-ip-failover-with-ucarp-on-centos-6/
http://www.pureftpd.org/project/ucarp