Take a Load Off

We all know that uptime is the lifeblood to the web economy. When a visitor browses a website to buy a product or search for information and the page loads up fast - joy. If it doesn't - burn. Load balancing is one method to ensure websites keep humming and visitors keep coming back.

Load balancing, basically is a technology used for dividing the work among two or more identical servers. The technology groups a number of identical servers, known as hosts, in a cluster and divides application requests among them. That is, managing the traffic so that no one server gets overloaded ensuring availability 24x7x365.

A load balancer, as the name suggests, balances data across multiple servers and sites, and directs Web traffic to the nearest, most available server. But it doesn't stop there. Most load balancers also offer failover services, cluster management, traffic routing and geographic load balancing across multiple sites and POPs.

The load balancer first defines a virtual cluster that consists of a number of actual servers. Typically, an administrator would set up an IP address for the virtual cluster, and all web traffic is directed to that address. Then the load balancer distributes requests to the servers in the cluster using an algorithm that determines how much traffic each server gets. There are several ways requests can be directed:

· If your primary server crashes, requests could be directed to your back up server

· Requests can be content driven

· Priority levels may be assigned. For example credit card purchases can take precedent over a visitor's request

· In the event of a natural disaster, requests can be sent to a server in another facility or another city

Load balancers come in three basic types. Among the earlier models was the "black box" appliance such as Cisco Systems LocalDirector - a PC-based product with Ethernet cards and software embedded in a UNIX operating system. The second is the software-based solutions that typically run on a dedicated server. Resonate's Dispatch was one of the earlier models. Finally the "smart" switch solution is built in to a LAN switch, a computerized box that delivers data from one segment of the local access network to another. Alteon WebSystems (acquired by Nortel Networks) is one of the leading switch-based vendors.