The BALUG.org Virtual Machine (VM) balug / balug-sf-lug-v2.balug.org which also hosts most all things, not only BALUG.org, but also SF-LUG.org (excepting it's lists) and BerkeleyLUG.com, I'm intending to upgrade the operating system soon. Expecting some modest outages with some service restarts and reboots, etc. But expecting for the most part it will remain up. I did also earlier upgrade "vicki" https://lists.balug.org/pipermail/balug-admin/2020-February/001016.html just fine, and also successfully completed a dry run test upgrade: created LVM snapshot of the running balug VM, copied snapshot to LVM volume, built VM around that volume - and configured to be highly similar to balug (differing only in Ethernet MAC address and VM related UUID(s) and name and networking (different subnet/network/vLAN)), disabled network link at VM before "powering up" the VM, reconfigured network so as to not conflict with balug, disabled services (most especially anything that would attempt to send email), enabled network link and networking, went through the full upgrade process - all went well, no issues of any significance encountered.
Anyway, now I move on to the "real deal" (the actual balug VM). I'll report if any significant issues come up - otherwise presume all has gone fine and the upgrade will be completed soon (likely today).