How to Handle Adding 2nd Node to single MariaDB Galera "cluster" already in production? I currently have a a single instance MariaDB 10.2.6 Galera instance sitting in production. For reasons, I botched the upgrade from 5.5.56 to 10.2.6 on a previously 4-node cluster.

Is there a way to minimize the downtime that will occur when adding a new MariaDB Galera node to this new cluster?

Could I mysqldump the data and have it rsync the rest of the data?

The grastate.dat on the primary node is as follows

# GALERA saved state
version: 2.1
uuid:    a75b7820-2b7c-11e3-9356-763f33730b6c
seqno:   -1
safe_to_bootstrap: 1


Or am I out of luck in terms of minimizing downtime?
The best way would be to use the xtrabackup-v2 SST method.  It is non-blocking for most of the transfer; there is a short blocking period at the end of the transfer when it has to get the latest data from the donor, but that is usually only a few seconds at most.  The other SST methods would need the donor to be offline for a much longer period since they aren't designed for online transfers.