We are running a busy self service ERP for growing 400k employees, on a single database instance for 7 years now. Currently at 256gb ram, 8tb database, 32 P9 cores. I got 99 problems but the single database server ain't one of them!
Because then it won't scale.
And the moment you do you run into other bottlenecks.
We're not running the DB in Kubernetes though.
For DR, Entire stack is being continually synced with a set of hot server in separate datacentre. We run a fully DR exercise yearly and it works well. It's a fairly proprietary AIX / DB2 method though so not sure you'd find value unless you're using the exact same technology stack :-/