Test Center guide: Load balancers and Web accelerators
Barracuda, Citrix, Coyote Point, F5, Kemp, and Zeus offerings stretch from no-frills appliances with basic load balancing to kitchen-sink solutions with rule-based traffic management, application security, and application performance optimizations; here's how to pick 'em, based on our tests
From the early systems that were built on PCs with two Ethernet cards, load balancers have evolved to include up to 24 switched Ethernet ports and custom ASICs running routing rules at gigabit wire-speed. Other systems add protection for Web servers and other types of application servers, guarding against buffer overflows, denial of service, and other hacker attacks. Still others add the ability to route incoming traffic to specialized clusters of Web servers depending on the needs of the customer, so that e-commerce requests go to one cluster while video viewing is done on another. Finally, a more recent trend is to add Web acceleration technologies, including HTTP compression, caching, and consolidation of TCP/IP requests from hundreds to a few.
The bigger question is whether you want all of these capabilities in the same box as your load balancer, when you may very well already have another box that does the same thing. SSL termination is a common addition because it simplifies load balancing. WAN optimization is also a good fit, considering that functionality needs to be outside the firewall along with the load balancer, and the right kinds of optimization can really improve the user experience, which is one of the main goals of load balancers. Other features such as firewalls, anti-spam, and site-to-site acceleration are less obviously a good fit. These are things that might be better done with separate boxes.
Software, appliance, or switch
Load balancers can be divided into two general categories: software- or appliance-based systems (running on Linux or Windows and Intel- or AMD-based hardware), and switch-based systems that make use of proprietary operating systems and hardware.
The software- or appliance-based systems are easy to add functionality to, but they are limited in throughput, since they rely on the two to four network interfaces installed in the appliance. Switch-based load balancers often have 24 or more ports, and offer gigabit or higher performance on every port. In the last few years, switch-based products have come to offer the same kinds of extended functionality as appliances, including support for e-commerce, additional security features, network acceleration, geographic load balancing, and more.
Once owned by software-based solutions, the low end of the market is in flux. First, the added cost of hardware on Linux- or Windows-based appliances is offset by the dramatically reduced time to configure the system. Second, the entire "commodity" category is getting smaller as time goes by – the ready availability of ASICS (Application-Specific Integrated Circuits) means that switch-based load balancers can be inexpensively made. As prices of switch-based load balancers have dropped, and more organizations have started delivering Web-based applications both internally over high-speed connections and externally over a slow Internet links, switch-based products are coming to dominate the market. However, appliances offer a low starting cost, are easily expanded with SSL acceleration boards and other add-ons, and still have a place, especially for organizations with no need for multiple gigabit ports.
If you want to spend the time, you can use an existing Windows server and WSLB (Windows Server Load Balancing) software, or with Linux installed and add IPVS (IP Virtual Server) or BalanceNG load balancing software to create your own load balancer. However, unless you’re paid a lot less than the average admin, the time you spend configuring the Linux server and the IPVS software will more than offset the cost of a small appliance, some of which are available for less than $2,000 including the hardware.