Redundancy, Standby reads values although the server is online
It is fundamental for the redundancy, that the standby server also collects the values from the process in order to be able to switch without any loss of data in the case of a server crash!

Basically:
Server (main) and standby server both have a process communication so drivers are started an communicate with PLCīs!
The server serves all clients as well as the standby server with data to be displayed and stored!
So the standby server gets the values to archive and so on from the Server, as long as both are online.
In the time where the server is online the standby server only fillīs its puffer (NET_TIMEOUTMSEC -> Default 30 seconds) with the values it gets from itīs drivers!
The standby server does this in order to be able to fill e.g. the archive with the values after a server breakdown has been recognised ( three watchdogs [NET_TIMEOUTMSEC / 3] arenīt answered)

Example:
NET_TIMEOUTMSEC=30000 (Default)
Every 10 seconds a watchdog is send -> if three watchdogs arenīt answered by the server this is meant to be offline.
The standby server has a puffer for NET_TIMEOUTMSEC and fills up all the modules with its pufferd data ( no loss of data ) and it will be the new server!