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  Web Server Balancing: An Act Worth Watching By Greg Yerxa As the Web grows and the number of Web surfers steadily increases, many companies are finding that their Web sites are overloaded and unreliable. Should they upgrade their server hardware or software? Not so fast! Web loadbalancers may provide a better alternative to constant server upgrades, which offer minimal performance gain at a high cost. Web load-balancers, or TCP/IP service balancers, can be an effective solution for your overburdened Web servers. The principl e is simple and (in some forms) already in use. Many sites have implemented Domain Name Service (DNS) in a round-robin fashion using more than one Web server for a Web site. However, this method of load-balancing does not fully "balance" the load and cannot help determine the most capable server. It also cannot provide distribute d content on a variety of different servers.
In Network Computing's lab at the University of Wisconsin, we quickly and easily inserted a load-balancer into our existing server configuration. Our server base consisted of two Pentium Pro 200s and two Pentium 90s running the same Web server with identical Ethernet connections. After finding a length of cable to use with the new hardware, we unplugged the server su bnet from the network and ran the network feed through the load-balancer. (See diagram on page 103.) We then reconnected the subnet to the network via another network port on the load-balancer, and the servers functioned again. Initially, the load-balancer did nothing more than act as a bridge. Next, we configured the balancer. First-time setup is normally handled with a serial connection. However, some vendors have included video and keyboard connectors on the back of the load-balancers. After defining each of the Web servers as physical servers on the load-balancer, we defined the virtual server(s) and the balancing method--a separate IP address for each virtual server and a few keystrokes. We chose a weighted selection method, assigning more priority to the Pentium Pros and reducing the strain on the less-capable Pentium 90s. This entire process seemed a bit too easy, so we conjured up a Perl script capable of pounding the new virtual Web site. Still not satisfied, we reached up and yanked a server 's power cord from the wall and, sure enough, the script paused for what seemed a millisecond and then continued. After pulling out a few other power cords, the benefits of this device became apparent. With minimal setup time and even less effort, we added another dimension of reliability to our Web servers. If service is your game, these devices could pay for themselv es and their server equivalents. Reasons to Strike a Balance When you are faced with an overloaded Web server, you need to determine if a Web load-balancer will help. If you are just beginning to provide Web content, a simple memory upgrade might provide all you need. Web servers work much faster when the amount of memory on the server lets them cache commonly requested pages. However, if you push the limits on your machine, you may run out of upgrade options quickly. If your budget can manage the addition of a server or two and a Web load-balancer, this alternative might be your best option.
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Updated July 25, 1997 |
