Thanks very much both @pfaffman and @Poster_Nutbag - super useful!
EBS does sound like a better option - means we’d avoid diverging from discourse/docs/INSTALL-cloud.md at main · discourse/discourse · GitHub.
Following from your advice I think I’m going to go for RDS but to pin to a specific commit of the discourse_docker repo. Whilst it sounds like that will make upgrades more complex, I’m hoping it means that if we do have a problem with the server we’ll have everything safe on RDS and fairly swiftly be able to the same working state without a manual restore.
(We could achieve the same thing with EBS I think, but with volume encryption and unix magic to mount/dismount the volume between instances I’m a bit scared of the process of automating that)