Tip

Blade server load balancing

Gopala Tumuluri

As IP and Web applications have become mission-critical for the productivity and profits of organizations around the globe, implementing always-on, highly secure and scalable server farms has become a critical requirement. Businesses cannot afford application downtime, or even poor performance, which costs from thousands to millions of dollars in lost productivity and profits. Adding to the risk of downtime is the ever-increasing threat of denial of service (DoS), virus and worm attacks by malicious users trying to cripple the mission-critical applications.

Load balancing has evolved into a solution of choice to provide high availability and robust security to IP applications. Load balancers allow IT managers to leverage commodity servers and intelligent Layer 4-7 technology to build highly sophisticated application infrastructure for the mission-critical needs. Additionally, load balancers act as the last line of defense

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to applications and servers by preventing and defeating high-speed attacks.

Server farms experienced tremendous change in the past few years as they migrated from the traditional large mainframe systems to the highly flexible and cost-effective blade servers. Blade servers are easy to deploy and simple to maintain, and can be added and removed on demand resulting in capital and operational cost savings. By combining blade servers with intelligent load balancing, IT managers can create high-capacity and secure virtual server farms.

Load balancers are completely transparent to the applications and server farms. They receive all client requests and distribute the requests efficiently to the "best" among multiple servers. Load balancers consider server availability, load, response time and other performance metrics in server selection. By performing sophisticated "health checks" to the servers and the applications, load balancers identify unavailable resources in real time and adjust the usable pool. Server capacity can be added or removed on demand without impacting the applications. When the demand grows, administrators "slide" in new resources and configure the load balancer to use them.

Many load balancers provide content inspection and switching intelligence. Just as IP packets are switched to the right destination using information in the IP packets, load balancers can switch application requests to the right server(s) based on the information contained in the application messages. Content switching eliminates the need to replicate all content on all servers and optimizes overall resource utilization and application performance. Content switching can be based on URL, HTTP headers, HTTP cookies, SSL session IDs or XML keywords.

One of the crucial benefits of load balancing technology is its ability to protect server farms and applications from attacks. Load balancers act as a connection proxy to the server farm and shield the servers from initial client communications. Only after receiving sufficient information from the client to validate the legitimacy of the requests does the load balancer forward the client connection to the "best" server. Leveraging high-speed content inspection functions, the load balancers also filter out viruses and worms that spread through the application messages.

Load balancers are inherently flexible and support numerous protocols, applications and content types. As applications evolve and the mechanisms to scale and secure these applications change, the load balancers can be easily upgraded with the newest intelligence to meet yet unknown needs. As you deploy blade servers, it is the best time to consider load balancing to solve the availability and security challenges. Size, capacity and modularity of blade servers make the strongest case for using load balancers.



About the author:
Gopala Tumuluri is a Product Marketing Manager at Foundry Networks, a maker of Internet routers, Layer 2 switches and traffic management products located in San Jose, Calif. He can be reached at gopala@foundrynet.com.

This was first published in June 2004

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