Tomorrow I'm going to upgrade several of the OpenStack control nodes to
Debian Buster. Due to version incompatibilities, Buster and Stretch
nodes can't cooperate in the same cluster, so I will need to switch
service between clusters a couple of times.
If things go really well, this will cause only brief hiccups in the
OpenStack APIs. More likely, though, things will get a bit tangled up
and Horizon will misbehave for 20-30 minutes during the transition.
The first switchover will happen between 14:00 and 15:00 tomorrow; the
second switch will follow an hour or two later.
-Andrew