Configure MySQL Master-Master Replication
https://support.rackspace.com/how-to/mysql-master-master-replication/
Single slave - multiple master MySQL replication - Database Administrators Stack Exchange
https://dba.stackexchange.com/questions/40379/single-slave-multiple-master-mysql-replication
How To Set Up MySQL Master-Master Replication | DigitalOcean
https://www.digitalocean.com/community/tutorials/how-to-set-up-mysql-master-master-replication