Two of the more popular solutions are MySQL Master HA and Percona Replication Manager.
MySQL Master HA
MHA is based on a set of Perl scripts that monitors for replication and server health. When a failover scenario will happen, it can do automatic failover to a slave OR from a selection of slaves you have configured to make as the new master. The good thing about this is, after the initial failover, there will be no succeeding attempts to fail back, this is to protect your data and consistency of the cluster. You can also configure to only have manual failover for scheduled maintenance and the like. Between PRM and MHA, MHA is really easier to manage.
http://code.google.com/p/mysql-master-ha/
Percona Replication Manager
PRM is based on …
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