Hi JasonLLM,
I will explain this in context of using ONLY the Service Desk Manager application and none of the other applications that are a part of the solution. For Advanced Availability (referred to as "AA") you would need at least 5 servers to really use the AA functionality. Those would consist of the following:
1. DB Server for the MDB
2. Background Server
3. Standby Server
4. App server 1
5. App server 2
You would install Service Desk on the Background, Standby, App1 and App2 servers (so 4 in total).
The Background server takes the place of what was previously the "Primary" server. It will handle all of the "background transactions" as we call them - things like firing events and notifications, checking for conditions, etc. The Standby server is just that, its standing by in case something happens to the Background server, in which the Standby server can be "promoted" to be the background server, while work is done on the original Background server. The end user traffic will ONLY hit the App servers, in which you would want to use something like an F5 load balancer to balance the load between the two (or more) app servers. The end users do NOT hit the Background or Standby servers. The only reason you would hit the SDM URL on a background server would be to log into the GUI to configure the standby and app servers via the GUI (as we no longer use pdm_perl pdm_edit like we used to in versions prior to 12.9).
The biggest difference between conventional (Primary/Secondary), and AA (Background, Standby, App servers), is that in a conventional configuration, ONLY the primary server talks to the database, but in an AA environment, each server independently talks to the database and has its own virtdb process and db agents, thus making for better performance in most environments.
I hope this helps give you some insight into using the AA configuration with SDM
Thanks,
Jon I.