Same here, and as long as you understand how mysql replication works it's not too much effort to deal with. Performing the initial sync without downtime is a bit tricky, but can be done with a well-designed database and some thought. Basically you need to at least temporarily make the bulk of your data read-only, so that you can do most of the data transfer while things are running, and then only briefly lock tables on the source server for long enough to copy the stuff that has changed since the dump, and grab the binlog position. Then you copy that stuff over to the slave as well, update the slave to the correct position, and then start the slave.

That's master/slave, but to get master/master, all you need to do is start a slave on the original master and point it at the current master position on the original slave (which should be static since it isn't yet accepting any queries directly). These posts may be helpful:

https://www.digitalocean.com/community/tutorials/how-to-set-... http://plusbryan.com/mysql-replication-without-downtime

Once it's running, as long as you're not running autoincrement queries or other things that can conflict on both servers at the same time, without taking appropriate precautions, it should chug away without any intervention.

If something does go wrong, you can often figure it out by looking at the slave status, fixing the inconsistency manually, skipping the bad query, and then starting the slave. If not though, you can always just re-synchronize from scratch. Or even better, run your databases off of an LVM volume, then take regular snapshots. (IE snapshot, make a tarball of the snapshot of the mysql directory, then remove the snapshot.) That will give you a consistent backup, even with the server running. On an SSD, the temporary added latency probably won't be noticed, especially if done off-peak. Then if anything goes wrong, you can restore from the snapshot, and it should catch back up to the master from the snapshot's position automatically (as long as your expire_logs_days setting in my.cnf is longer than the duration since the snapshot was taken).