In nGrinder version 3.1, we introduces nGrinder controller clustering, which make the performance test can be executed in multiple controllers with better controller performance and support multiple set of agents(named region) to be used.
Below is the architecture without cluster supports.
If you enables custering mode by configuring the system.conf(See link) and install nGrinder into multiple machine,
the system architect is chagned as below:
Each controller can serve nGrinder web content equally but handles the different tests per region in the background.
We don't provide any session clustering by default. So you may suffer the login problem by the different session b/w controller. Because the session stored in a controller is not replicated to the other controllers. You may need to configure this by referring Tomcat Session Clustering Guide or using the sticky session on L4. If you are not a expert on this, Just let users to connect only one controller. It's the easiest. :-)
How to configure the clustering? Check Controller Clustering Guide