In our OpenDev NSX environment, we have 3 vSphere clusters: each cluster has 3 ESXi hosts.
During the NSX upgrade from 6.2.3 to 6.2.4, we see the following message when we tried to upgrade the ESXi cluster which NSX Controllers are running on: DRS recommends hosts to evacuate.
After a quick investigation, I realised that the issue is due to default DRS anti-affinity rule for NSX controllers. This anti-affinity rule prevent any host in management cluster from going into maintenance mode as we have only 3 ESXi hosts in this cluster.
So I just temporarily disable the NSX controller anti-affinity rule so that EAM (ESX Agent Manager) can continue to update the ESXi hosts VIB to the new version.