How much data? I keep hearing k8s isn't usable becasue sometimes there is to much data and it can't be moved around.

In the managed k8s space, the data is on a PVC in the same availability zone as the node it is being mounted on. If the node dies, the volume is just mounted on to a new node in the same zone. There is no data movement required.

While I've not played with k8, I did run stuff in Google's Borg for a very long while, and that has a similar architecture. My team was petabyte scale and we were far from the team with the largest footprint. So it is clearly possible to handle large scale data in this type of architecture.

The simplest approach I’m aware of is to create the k8s cluster and databases in the same datacenter / availability zone.