Upgrading an existing Horizon Connection Server is a straightforward process that typically requires no more than a few minutes to complete, not counting the time required to plan the operation. Regardless, it is important to block access to the Connection Server while the upgrade is being performed to ensure no Horizon clients attempt to connect to it, or at the very least to perform the upgrade during a period of time in which the Connection Server is not expected to be used.
If you are using a load balancer to distribute traffic among multiple Horizon Connection Servers, the easiest way to block access to the Connection Server is to remove it from the load-balancing group. This prevents connections from being sent to it, while at the same time being transparent to the end users.
Do not disable the Connection Server network cards...