If one Web server fails or is taken off line, the load balancer cuts it out and shares the load among the survivors. We review seven load-balancing products . The database and application servers that sit behind the Web servers do more internal processing and don't communicate with the same intensity. They typically use a technique called server clustering to keep operations reliable. One server in a cluster takes over operation from a server that falters.
Redundancy is just as important inside the server.
One valuable technique, server monitoring , is underutilized. Practically all server-class computers can report internal cabinet temperature, drive status, intrusion into the cabinet, and other factors affecting reliability to network management consoles. There are other high-availability techniques that make sense in specific situations. If your Web pages are taking orders and credit card numbers, you can still use caching to deliver logos, menus, ads, and other page elements that aren't interactive, but you have to add more Web servers and more application servers to process transactions. If your site handles a lot of e-commerce transactions involving SSL encryption, consider encryption acceleration products, such as Intel's NetStructure 7110n.