A follow up from T315271 would be to document what is needed to depool a whole DC in MW in case all the databases from a given DC go down (or the master fails).
I have assigned this to @tstarling but also pinged @Krinkle at T315271#8177397 so feel free to re-assign if needed.
If possible, please could you add that to https://wikitech.wikimedia.org/wiki/MariaDB#x2
Thanks