DR For MySQL multi master nodes
For "dual-master", it is best to write to only one of them.

Failover involves (mostly) pointing the clients to the newly-writable master.

MHA automates the process; read about it.

In my opinion, dual-master only handles a limited number of failure scenarios, namely the crash of a server.  The next step is to separate the masters so that a power failure, earthquake, tornado, etc cannot take out both at the same time.  But then you get into the "split-brain" problem, wherein you can't tell which Master is the surviving one because you can't check both of them.  (And both might be surviving!)

Next comes Galera, which needs 3 nodes, and is self-healing.  It comes standard with MariaDB.

If you want the MySQL path, then you need to get beyond 5.6 in order to get a reasonably robust "Group Replication" / "Innodb Cluster".  (8.0 is desired for that.)