The release of new versions of VMware Horizon 8 each quarter of the year (to provide new features and resolve any security holes) entails the need to have a consolidated, conservative update procedure with the least impact on users.
Below I report the procedure that I am using successfully.

User impact:

• Users already connected to the VDI do not encounter problems or disconnections
• Users who need to connect during update activities may have problems (normally a maintenance window is declared)

Steps

• Restarting the Connection Servers Operating System (One at a time is a step preparatory for committing any pending Windows updates), after each reboot check from the Horizon web console that everything is ok
• Disable Provisioning
• Shut down all three Connection Servers
• Snapshot of the VMs hosting the Server connection
• Turn on the Connection Server (One at a time), after each reboot check from the Horizon web console that everything is ok
• Backup DB Adam (C:\Program Files\VMware\VMware View\Server\tools\bin\vdmexport.exe > vdmconfig.ldf)
• Disable and Updating one Connection Server ( disabling the Connection Server being updated puts the connection server offline for the load balancer on the top of the connection servers and it is not used for authenticating users and assigning VDI) and after upgrade enable the Connection Server.
• Repeat the previous step for all Connection Servers
• If necessary, reapply the customizations
• Check from the console that everything is ok

After the horizon upgrade, test the Desktop Pool:

• Try a connection from internal
• Try a connection from external
• Delete a VDI machine
• Publish a new Master Image

For upgrading three Connection servers all steps necessity of two hours
During the activities, the users connected to the VDI do not encounter any problems

The next step, after complete the Connection Servers upgrade, is to update the Horizon agent on the master image and delete the Connection Servers snapshot