> So, if I understand well, if I have 3 MariaDB Buster nodes in a cluster, > I just need to dist-upgrade them to Bullseye, and it will automagically > just work and upgrade to Galera 4? If so, that's just great, because > during our last discussion in Brazil, you told me about something a way > more risky (ie: turn off 2 nodes, upgrade the 3rd one, then upgrade node > 1 and 2).
Yes, after we spoke 1,5 years ago Galera has started to support rolling upgrades from 3->4. I have personal experience that it works. So keep all 3 nodes on. Upgrade fully one node, wait until it joins and syncs and cluster is PRIMARY again, then proceed with the 2nd node etc.
