Round Robin

Round-robin load balancing is one of the simplest methods for distributing client requests across a group of servers.

Going down the list of servers in the group, the round-robin load balancer

• forwards a client request to each server in turn.
• When it reaches the end of the list, the load balancer loops back and goes down the list again (sends the next request to the first listed server, the one after that to the second server, and so on).

The main benefit of round-robin load balancing is that it is extremely simple to implement. However, it does not always result in the most accurate or efficient distribution of traffic, because many round-robin load balancers assume that all servers are the same: currently up, currently handling the same load, and with the same storage and computing capacity. The following variants to the round-robin algorithm take additional factors into account and can result in better load balancing:

Weighted round robin—A weight is assigned to each server based on criteria chosen by the site administrator; the most commonly used criterion is the server’s traffic-handling capacity. The higher the weight, the larger the proportion of client requests the server receives.