Host clusters can be upgraded after the NSX Manager and all of the NSX Controller Nodes have been upgraded. The host clusters upgrade is a vSphere cluster-level operation, but there is no downtime required, as the VMs are migrated off before completing the upgrade. Verify that you have enough resources to accommodate VM movement within the cluster.
There is no hard requirement to upgrade all clusters in the same maintenance window, as NSX Manager and NSX controller node communication to the hosts are backward compatible. It is important to understand how long it takes to reboot an ESXi host, as this will impact the overall length of the maintenance window.
In addition, the following prerequisites need to be satisfied: