Automatically and robustly restarting a Galera cluster
I would say the best practice would be to ensure that one node is always still running, when the others have stopped normally. (systemctl stop mysql/mariadb)
Then restart one of the previously stopped nodes, and when that restarted node reports in logfiles that it connected to the running old node, and that it's ready to serve connections, you may restart the old one still running.
If all nodes have been stopped, you need to figure out manually which is the newest node (by using (ubuntu):galera_recovery, note the highest change no.)
Maybe even have edit the safe_to_bootstrap line in the grastate.dat file.
That node then needs to restart the cluster (create the new unique ID for the others to connect to) (by using (ubuntu): galera_new_cluster).
The remaining nodes simply start db with 'systemctl start mariadb'.
Sounds as if there's a reason they didnt yet built that in to systemd ;) ?