From what I understand, there is no official non-third-party tech to do multi-master pgSQL & even more so that applies to Redis.
Is it really not possible to tell Discourse about such environment and tell it not to worry about it &| ignore it?
If it’s not and @devel read this, then I suggest - many I’d think will appreciate - to “enhance” Discourse that way - so it does all the necessary checks but does not fail but starts & run on such read-only “data”.