I've been using LinuxServer's Unifi-Controller docker for a long time to manage my unifi devices. However, this has been deprecated and to keep up with new releases, there is a requirement to install a Mongo database docker and a newer Unifi docker. This sounded like a bit of a faff but I thought I'd give it a try before succumbing to a physical controller device. The process did not go well, and I couldn't seem to get the systems to work together.
However, in searching around for solutions, I saw there was a new 'all in one' option, the UnraidReborn/issues">Unifi-Controller-Reborn docker from PeteAsking. (find it in the Apps tab). I gave it a whirl and was able to get my old setup running in a shiny new Docker. Along the way were a few learnings that I thought I'd log here for posterity.