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Web Server Redirectors Balance Your Web Load

By Greg Yerxa Web load-ba lancers, or more appropriately, TCP/IP load balancers, are quickly becoming an alternative to expensive Web server upgrades. Offering a plethora of features and options, these load-balancers eliminate many of the pitfall s--including downed sites and swamped servers--of today's largest Web sites.

However, the products on the market vary a great deal, as we found in our testing of five hardware and software solutions that balance Web loads. We tested Cisco Systems' LocalDirector 1.2.5, F5 Labs' BIG/ip2 1.5, HydraWEB Technologies' HydraWEB Load Balancer 1.2, Resonate's Dispatch 2.0 and RND Networks' Web Server Director Pro.

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Because these products generated similar performance statistics in our tests, we needed to look further into each balancer's feature set to determine the leaders of the pack. We exam ined different Web load-balancing methods--round-robin, cyclic, fastest response (ping), resource-based and proprietary--plus server flexibility. We also looked at scalability in terms of the number of virtual and real servers, as well as Simple Network Management Protocol (SNMP), e-mail and real-time performance monitoring.

In Network Computing's lab at the University of Wisconsin in Madison, we set up two Windows NT Web servers and began hitting the load-balancers to determine their strengths and weaknesses. In our tests, HydraWEB HydraWEB Load Manager 1.2 was the big winner, boasting the most advanced and configurable device. Resonate Dispatch 2.0 followed as a close second, with its high flexibility and management features. RND Networks' Web Server Director Pro received our Best Value award, offering the most bang for the buck.

HydraWEB Technologies HydraWEB Load Manager 1.2
Hy draWEB Load Manager 1.2 receives the highest marks primarily because of its flexibility and ease of use. Offering the richest feature set of the five and performing well (just behind Cisco LocalDirector in the longer tests), HydraWEB comes ready to serve. Easily navigable configuration utilities and server-side agents were a breeze to install and use--and much better than Cisco LocalDirector's and BIG/ip2's balancers. Other impressive features include HydraWEB's Logical Content Clustering, which enables detailed configuration of each cluster and its servers. It also serves as the active communicator between primary and secondary units acting as a failover. Although HydraWEB failover is more difficult to install than BIG/ip2's, communication between the primary and secondary includes information about each node--not simply a signal for failover.

Initial configuration is automated for the most part, with boot-time scripts in place. After being prompted for crucial information and a simple reboot, we had Hy draWEB set up and ready to go. Although HydraWEB's terminology is complicated, the documentation materials--which consist of a user's manual and many helpful notes spread throughout the configuration utility--are more than adequate. The text-based configuration utility we used to make changes to the system was well organized.

For each real server in a cluster, HydraWEB lets you configure scaling factors and additives for calculating the Multiplexer Load Average, or PLA. (When HydraWEB calculates the PLA, it includes properties such as load average, CPU utilization, service speed, resource utilization and shutdown status.) After each server's PLA is calculated, you can use administrative weights and scaling factors to skew the PLA.

For example, you can set a particular server's scaling factor for greater than one, so that other servers will be used to their fullest extent before the skewed server is used. By altering the load-balancing, you can divert users from a particular server and facilitate back ups or other server-intensive operations that would slow a server and its responses to clients.