Is it possible to install harvester VMs on top of harvester cluster? Could be very good for tests later.

do you mean install harvester on top of a harvester cluster? that is not documented though but it can be done😄

Yes! VMware vSphere has nested ESXi support. It would be much easier to test harvester upgrade in that case.

you can easily spin up a virtualized harvester cluster on a baremetal cluster as soon as you have enough hardware resources, we use a lot when testing some functions in daily devs

hardware resources not a concern for me. I am only aware that it is possible to use ISO to install harvester cluster one VM at a time, which is going to be slow for me. There’s cluster api provider for kubevirt, not such for harvester. I am not sure how virtualized harvester cluster could be spin up easily ..

Yes - I've run a Harvester cluster in VMs on my Harvester cluster built on NUC like tin.

Would that be too slow for you?