Product Documentation

The Round Robin Method

Mar 16, 2012

When a load balancing virtual server is configured to use the round robin method, it continuously rotates a list of the services that are bound to it. When the virtual server receives a request, it assigns the connection to the first service in the list, and then moves that service to the bottom of the list.

The following diagram illustrates how the NetScaler appliance uses the round robin method with a load balancing setup that contains three load-balanced servers and their associated services.

Figure 1. How the Round Robin Load Balancing Method Works

If you assign a different weight to each service, the NetScaler appliance performs weighted round robin distribution of incoming connections. It does this by skipping the lower-weighted services at appropriate intervals.

For example, assume that you have a load balancing setup with three services. You set Service-HTTP-1 to a weight of 2, Service-HTTP-2 to a weight of 3, and Service-HTTP-3 to a weight of 4. The services are bound to Vserver-LB-1, which is configured to use the round robin method. With this setup, incoming requests are delivered as follows:

  • Service-HTTP-1 receives the first request.
  • Service-HTTP-2 receives the second request.
  • Service-HTTP-3 receives the third request.
  • Service-HTTP-1 receives the fourth request.
  • Service-HTTP-2 receives the fifth request.
  • Service-HTTP-3 receives the sixth request.
  • Service-HTTP-2 receives the seventh request.
  • Service-HTTP-3 receives both the eighth and the ninth requests.
Note: You can also configure weights on services to prevent multiple services from using the same server and overloading the server.

A new cycle then begins, using the same pattern.

The following diagram illustrates the weighted round robin method.

Figure 2. How the Round Robin Load Balancing Method Works with Weighted Services