Linux Heartbeat

"Linux Heartbeat which is part of the High-Availability Project is a traditional method used for configuring a failover scenario. One server is the primary server taking requests. The second server is on standby receiving replication from the primary. Once the primary has a hardware failure and a heartbeat can no longer be detected by the secondary server, then the secondary server takes over the application IP and serves requests in the primary's place."

http://dev.mysql.com/tech-resources/articles/failover-strategy-part1.html