Kubernetes control the order of scale and upgrade for a StatefulSet

Question

I have the following scenario:

1. A StatefulSet with 1 replica
2. Update the template section and scale it in the same operation using helm as application manager
3. The order of operation is the following:
   1. Scaling to 3
   2. Update the replica with name 0

Because I cannot control to first update and after that scale, I am losing data because there is a specific logic in the new statefulset template.

Is there a way to control the ordering of those operations?

The service in question is Redis, we are trying to get from standalone mode (1 replica) to replication(HA) without losing data.

Answer 1

For the moment I resolved the problem using a helm pre-install job that is basically scaling the sts to zero, after that helm is coming with the update.

Answer 2

I am not Redis expert, but I think that solution below should help you.

I would try to install another Redis HA instance (B) next to the existing one (A), taking as a data source for B a snapshot of A's PV. This could to avoid losing your data. For more information you can read more about volume snapshots.

See also this related problem.