Sophos UTM and STAS - Collector and Agent on same machine? How to install?

Question

Hello, 
 I just upgraded our Sophos SG-210 on version 9.402-7 and read some information about the Sophos Transparent Authentication Suite. 
 After reading the guide, I have several questions. Just for information we have 3 DCs (Let's say SVR1 with all the roles and SVR 2 & 3 as replicas) in our company. 
 - Do I have to install the STAS Agent on every DCs? Or is it enough on SVR1? 
 - Do I have to install a Collector, is it mandatory? If yes, can I install it on a DC (SVR1)? Do I have to install several connectors? 
 - What would you do in my case as far as I have 3 DCs and 1 Sophos SG-210 as Gateway? 
 Regards, 
 DeltaSM

vilic · Accepted Answer

At least one collector is mandatory. That machine is communicating with UTM. Agents are required on every DC in AD, since you never know which DC will authenticate particular client. 
 I would go with SSO suite on SVR1 (collector+agent), and only agents on other domain controllers.

vilic · Answer

Backup collector in case that SVR1 is offline ?