[ovirt-users] Upgrade from oVirt engine 3.6 to 4.0 - clean install of OS?

I have oVirt 3.6 running on CentOS 7 (one engine, two hosts). Upgrading to 4.0 seems to require a fresh, bare install of CentOS7 on the engine machine - is this a correct reading of the upgrade guide? It seems bizarre to me I have to wipe a perfectly fine running CentOS7 machine to do this - that seems so Microsoft. Say it isn't so...