A load balancer distributes requests among multiple application servers, with a view to optimally utilizing the available servers. Besides providing scalability and performance enhancements, a load balancer also improves reliability. For example, many load balancers can monitor the status of the different servers they support, and if one of the servers stops responding, a load balancer is able to reroute requests to one of the other servers. By providing a unified virtual image to service requestors, a load balancer enables continuous access to multiple redundant servers for Internet-based e-commerce applications.
In IT infrastructures, load balancers have been used predominantly to balance traffic among multiple web servers. While the traffic they handle has been predominantly TCP-based, recently, some of these load balancers have also been used to handle UDP traffic. Cisco’s Local Director product is a very popular load balancer used in IT infrastructures.