Scenario: A Citrix Administrator has configured an HTTP load-balancing virtual server with Least Response Time as the load-balancing algorithm.
The administrator notices that requests to the virtual server appear to be using the Round Robin load-balancing algorithm.
What could be causing the virtual serer to use the Round Robin load-balancing algorithm?
The virtual server is in startup round robin mode. When a new service is added or enabled in a Citrix ADC (NetScaler) configuration, the system temporarily uses the Round Robin load-balancing algorithm regardless of the originally configured algorithm. This is known as the startup Round Robin mode, which ensures that new services are not overwhelmed by a sudden influx of requests during their initialization phase.
The virtual server on a NetScaler appliance gets into a Slow Start mode or a Startup Round Robin mode whenever a new service is enabled or a new service is added to the farm. The load balancing algorithm falls back to Round Robin method regardless of the configured algorithm on the virtual server. Least Connections is the default load balancing method. When configured, the appliance selects the service that has the least number of connections. For example, if the Least Connections method is in use and a new server is added to the server farm, the load balancing algorithm can cause the new server to be overloaded with requests, because it has fewer existing connections than other servers in the farm. To avoid overloading of servers, the appliance performs Slow Start. During this phase, the appliance distributes the requests by the Round Robin method regardless of the actual method configured. https://support.citrix.com/article/CTX108886/netscaler-load-balancing-slow-start-mode