Balancing the Web Server Load

By Francis Chu  |  Posted 2001-08-20

Balancing the Web Server Load

Server load balancers have become a critical infrastructure component for ensuring optimal performance of large Internet or intranet sites. Raw performance numbers are a useful comparison metric, but load balancing and management features and the ability of a system to integrate with different Web infrastructure components should play a more important role when choosing the best solution for the job.

eWeek Labs tested two server load balancers that illustrate some of these differences and how hardware- and software-based systems compare: Radware Inc.s hardware-based Web Server Director Pro 7.10 and the software-based Zeus Load Balancer 1.3 from Zeus Technology Inc.

Hardware-based products usually come in the form of a ready-to-deploy appliance, switch or router and are optimized for the task of load balancing.

An advantage to software-based systems is that IT administrators can install them on any system that will deliver the desired performance. The disadvantage is that these systems arent born to the task and thus may saddle the software with some performance overhead.

To test the performance of Web Server Director Pro and the Zeus Load Balancer, we used Antara.nets Flame-Thrower II Web-stressing tool configured with four server and four client ports to emulate client/server transactions in an HTTP environment.

Web Server Director Pro

Web Server Director Pro

With its advanced Layer 7 load balancing features, the Web Server Director Pro appliance is a good choice for larger sites with complex topologies. Version 7.10 now includes Radwares SynApps architecture, which includes health monitoring, traffic redirection, bandwidth management and application security features.

Typical load balancers use Internet Control Message Protocol pings to check server health. Web Server Director Pro goes further by also performing IP and application-level checks. Web page and content verification capabilities allow the load balancer to ensure that Web applications are functioning properly and can use this information to take servers out of service if theyre not.

Traffic redirection allows application-specific servers to be grouped into "superfarms" using a single virtual IP address. When a Web client seeks to access a specific application on a Web site, Web Server Director Pro will send the request to the application server in the right farm. Superfarms make it easy to manage large groups of server farms with servers running different applications.

Web Server Director Pro can also provide TCP port multiplexing, so Web servers with Web pages assigned to different port numbers can be load-balanced to a single IP address.

Web Server Director Pros support for Global Layer 7 traffic redirection allows the system to direct requests to the server farm closest to the requester based on the Layer 7 information contained in the URL. This will improve client response time and is especially valuable for large corporations whose contents are distributed in different data centers across large WANs.

Web Server Director Pro performed well in tests, turning in about 9,800 HTTP requests per second with 4,000 concurrent connections—very close to the maximum of 10,000-requests-per-second limit that can be generated by FlameThrower with four client ports.

The Radware system costs $24,500 and comes in a 1U form factor with eight 10/100M-bps and two optional Gigabit Ethernet ports. Multiple systems can be easily configured and managed through the Web, command-line interface or Radwares Java-based management tool.

EWeek Labs

// Executive Summary: Web Server Director Pro 7.10">

Web Server Director Pro 7.10


Radwares updated Web Server Director Pro is a powerful hardware-based server load balancer that is easy to use, manage and scale. Although more expensive than Zeus Technologys software-based solution, organizations with large Web infrastructures should swallow the cost to take advantage of the in-depth load balancing capabilities the Radware system provides.

SHORT-TERM BUSINESS IMPACT // The initial cost of Web Server Director Pro is high, but most shops will have the box up and running in a short time and will see immediate benefits.

LONG-TERM BUSINESS IMPACT // Multiple ports and gigabit uplinks ensure that Web Server Director Pro will be highly scalable down the road. Its a good long-term investment.

Includes Radwares advanced SynApps architecture and powerful Layer 7 load balancing of global server farms; system has small footprint; easy to set up and deploy.

Expensive; less flexible than software-based systems.

Radware Inc., Mahwah, N.J.; (201) 512-9771;

Zeus Load Balancer

Zeus Load Balancer

Zeus Load Balancer is worth a look for simpler sites, the budget-conscious and/or companies with Unix-based hardware platforms.

Zeus Technology sells Zeus Load Balancer only in a mandatory failover configuration for $10,000. (In contrast, a second Web Server Director Pro must be purchased for failover protection.) The Zeus software can be installed on any two machines running a Unix-based operating system such as Linux, FreeBSD or Solaris.

The fault-tolerant pairs depend on Domain Name System servers to direct incoming clients to the traffic IP addresses, similar to the virtual IP addresses used in hardware balancers. In the event that one of the Zeus Load Balancers fails, the other box will automatically take over all of its partners traffic IP address and active connections.

The processor speed and amount of memory on the hardware directly affect Zeus Load Balancers performance. We installed Zeus Load Balancer on a pair of Compaq 450MHz Pentium II-based DeskPro computers with 512MB of memory and running RedHat Linux 7.0. Using the Flame- Thrower tool, Zeus Load Balancer turned in about 6,600 requests per second (approximately 3,300 requests per second per box).

Zeus Load Balancer has a much simpler load balancing scheme than Web Server Director Pros. Managed through a Web browser, Zeus Load Balancer uses a proprietary locality-aware request distribution algorithm; all traffic is load-balanced using this algorithm. Administrators can configure which protocol and ports to load-balance, and rules can be set up so specific requests can go to specific servers. For example, we were able to create a rule that directed all requests for GIF or JPEG files to certain Web servers.

EWeek Labs

// Executive Summary: Zeus Load Balancer 1.3">

Zeus Load Balancer 1.3


The software-based Zeus Load Balancer is a simpler and less expensive system than Radwares Web Server Director Pro, but it requires more upfront setup and configuration. The Zeus Load Balancers performance is directly tied to the CPU speed and the memory of the system on which it is running.

SHORT-TERM BUSINESS IMPACT // It takes longer to set up the software-based Zeus system than it does to set up hardware-based load balancers, but once it is properly configured, Zeus will deliver immediate benefits.

LONG-TERM BUSINESS IMPACT // The Zeus Load Balancer scales according to the hardware platform it runs on, so positive long-term business impact depends on savvy selection of system components.

Provides content-aware load balancing capabilities; offers failover configuration without extra cost.

More difficult to set up than hardware-based systems; lacks real-time load- statistics monitoring.

Zeus Technology Inc., Santa Clara, Calif.; (408) 350-9400;

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