Yes, we are putting our production mysql (mariadb) into k8s. We use a stateful set and the data is stored on persistent volumes. Even if the pod or whole cluster goes down, the data remains. So far, I am finding it more stable than a bare metal setup. Because if the db instance fails, k8s kills it and spins up a new instance using that same persistent data disk. In the meantime, there is a read replica running on a different node that can take some failover.

We also have a job that runs nightly to make a dump of the db and store it in the object store and the persistent disk has a snapshot scheduled for every two hours and in both cases, we are backing up the binary logs, so we can do point in time recovery much like AWS's Aurora offering.

We may eventually switch to a mariadb Galera cluster where there are 3+ master pods that distribute the load and can stay available if one pod dies. But I haven't done the research on stability of that setup yet. A few years ago it wasn't ready yet, but I imagine it is by now.

You can actually run production ready db in k8s pretty easily. There is volume and stateful set and DNS, I could see limit to what it could run.