The vendors and offerings
Appliance vendors include Barracuda Networks, Kemp Technologies, and Zeus Technology. Coyote Point Systems, which was on the appliance side for a long time, now sells switch-based systems and offers some of the least expensive switch-based products available, still with good functionality.

Switch-based vendors include Array Networks, Cisco, Citrix (NetScaler), Foundry, F5 Networks, and Juniper Networks, though Juniper announced in January that it is discontinuing its product line (DX systems will no longer be available after July 24, 2008). These vendors provide high levels of functionality aimed at serving Web sites that are scalable and highly available.

Beyond the basic parceling out of requests to groups of servers, some load balancers also use several different methods to speed up responses to requests or to compress traffic, lessening utilization of bandwidth. One of the main optimization techniques is to group what would otherwise be anywhere from a few to more than 100 TCP sessions into one, using TCP session multiplexing or TCP session consolidation, depending on the vendor. Because the overhead of starting a session is fairly large, and some Web browsers can start dozens or even hundreds of TCP sessions to display a single page, multiplexing and session consolidation can improve performance substantially.

F5, Juniper, Citrix, and Zeus offer similar kinds of compression and acceleration technologies, which Barracuda, Coyote Point, and Kemp don’t offer. F5 has outstanding ease of use, even better than Juniper, which has some very easy-to-use automation technologies that make it very easy to secure a Web site by moving to SSL without recoding the site itself. F5 also offers an application security gateway, which none of the others do, although many users may already have this capability in a standalone appliance. F5 has added Web application acceleration since our last review was completed. Citrix offers the greatest variety of acceleration technologies, with Juniper a close second and Zeus not far behind, although the Zeus box is not as easy to use. Barracuda and Kemp offer good basic systems at very low prices, starting at less than $2,000, while Coyote Point has an excellent higher capacity system that still costs much less than the F5, Juniper, Citrix, and Zeus offerings with all the bells and whistles.

All the systems can perform the basic load-balancing tasks of creating virtual clusters and directing traffic based on content or type of traffic. All will work for creating a sophisticated e-commerce application or SSL-based corporate portal. Acceleration is very much a “your mileage may vary” kind of application: The type of Web server, whether TCP/IP session persistence is enabled, and the types of content being served will all have major impacts on the effectiveness of acceleration techniques.