Customers upgrading to or installing Web Viewer for the first time may be concerned about how resources should be allocated to accommodate a given number of concurrent/simultaneous users.
How to accommodate 100 or so concurrent users for 12.1 Web Viewer?
Upgrading from r11.5 Web Viewer to 12.1 Web Viewer for Windows Server and trying to accommodate the same user base.
All things being equal, you should be fine with 12.1 Web Viewer because 12.1 generally scales better than does 11.5. 12.1 Web Viewer timeouts are best left at the default values. Where more horsepower is warranted is with the Web Server - you should have 4G of RAM devoted to JVM/Tomcat or WebSphere. So, the general recommendation is to have the one 12.1 Web Viewer for Windows with 4G and a single DRAS.
You might later load balance to a second DRAS, should your workload/volume ramp up and create performance or other problems.