I also still want a 3 node setup for high availability as well! With the recent ram prices etc. I postponed it.

However the idea is simple. You setup a ceph cluster so the vm storage etc is shared across the cluster or your nodes. Then you can configure for each vm where it should start and where it can fallover to. Eg. Start a vm on node 1, but also allow it to start on either node 2 or 3 in case node 1 is down. Ceph cluster takes care of the rest.