While absolutely "zero downtime" is hard to guarantee in the face of massive catastrophic system failure, a distributed NoSQL database like Scylla should prove to be survivable with the loss of any one datacenter. (You'd have to knock out two of three, or all three datacenters to pull us down. Is that still possible? Sure.) I do recommend people put a lot of thought and some actual chaos monkeying into their "zero downtime" architectures.

https://www.scylladb.com/2021/03/23/kiwi-com-nonstop-operati...