You can apparently do that with Galera, but I haven't seen that in production.
What they're referring to is most likely MySQL's half-baked "circular replication". Some people claim it works for them. Personally I tried it once and the usual MySQL replication issues (desync, InnoDB deadlock) would create much more uncomfortable situations than in a Master/Slave setup.
With master/slave you at least stand a chance of having one half of the pair survive through a problem. With circular replication the cluster would lock up hard almost every time for us, and - to add insult to injury - leave the pair inconsistent after recovery.
I think the confusion here is based on the difference between "multi-master" replication and "master-master" replication. MySQL doesn't support the former, where a machine can be a slave of more than one master, but it does support (like you eluded to) having two masters (usually one writable, one read-only) in a loop, which MySQL folks call "master-master" replication.
You can apparently do that with Galera, but I haven't seen that in production.
What they're referring to is most likely MySQL's half-baked "circular replication". Some people claim it works for them. Personally I tried it once and the usual MySQL replication issues (desync, InnoDB deadlock) would create much more uncomfortable situations than in a Master/Slave setup.
With master/slave you at least stand a chance of having one half of the pair survive through a problem. With circular replication the cluster would lock up hard almost every time for us, and - to add insult to injury - leave the pair inconsistent after recovery.