Most of you know, that it is possible to synchronize MySQL and MariaDB servers using replication. But with the latest releases, it is also possible to use more than just two servers as a multi-master setup.
Most of you know that both MySQL and MariaDB support replication in a hierarchical master-slave-setup, to propagate changes across all connected servers.
But with the latest releases, a slave can have more than one master.
The keyword: Multi-Source replication
It is supported from MySQL 5.7 and MariaDB 10.0 on, and this article describes how to set it up.