I had seen the SKIP_POST_DEPLOYMENT_MIGRATIONS doc. What I had really missed was this post that shows how to do zero downtime deployments with launcher:
So now I have to think about that, now that I know that it is feasible. If I do it, I’ll update MKJ's Opinionated Discourse Deployment Configuration with what I do.
I’ve been having lots of trouble getting worked up about it when I am providing four, some months four and a half nines of availability on a service that I run for free in my spare time. It’s a testament to the quality of Discourse development that I can do that on a tests-passed policy, including things like the extra minute or so of downtime I saw this time, and sometimes rebooting the host for security updates.