>what if the whole zone fails and all DB containers are shut off?

I agree that the container clustering world tends to focus on stateless scenarios, conveniently ignoring the "hard stuff". However, that doesn't mean it can't be done. k8s can be told to maintain persistent volumes that can be claimed by containers. This mechanism can be (has been) used to implement "real" DB HA. e.g. see this talk : https://www.youtube.com/watch?v=Zn1vd7sQ_bc