Yeah, be it a DNS change, or booting a temporary docker ngnix container listening on the same port that serves something is the easy part.
Right now the most difficult part of this is a static export with interactivity disabled and a banner added, respecting topic, post, category, index pages (search can be down). Then streamlining this replacement into the upgrade process, however that is easy enough.
Searching the forums for static export, doesn’t really seem it is a thing. I’ve made a Discourse API client already for a prior project, so could code something up that doesn’t emulate the design I guess.
Another factor of serving a static export for this purpose would be ensuring that the static pages are not cached by browsers and not cached by search engines.
I wonder if How do I export the complete forum as static html pages? - #3 by wangerin would suffice, however seems it would still require interactive elements disabled and a banner injected.