(mysql) Database replication between 2 DB while 3rd DB as backup
Dual-Master, where you write to both masters, is full of problems.  You need to carefully set the two auto_increment_* "variables".  You need to make sure users cannot insert the same PRIMARY or UNIQUE values into different masters.  If 'East' goes down, the Slave is hard to reconnect.  If a hurricane hits the East, you lose both the master and slave there.  Etc.

A slight improvement is "Dual-Master, Single writer".  That is, you have the configuration you described, but clients never write to more than one of the Masters.  The configuration is more stable, but the failover process is perhaps more complex.

Instead, consider Galera (in MariaDB or PXC), which solves many of the problems.