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As a result of the economic slowdown, the load balancer industry has gone quiet and growth seems to have stopped. At least one vendor has gone out of business, although the load balancing industry seems to have fared slightly better than other Internet-related industries. Within the market space, the SSL (Secure Sockets Layer) accelerator business has been doing even better. Although SSL accelerators perform separate functions than load balancers, their functions are intrinsically linked.
SSL accelerators are network appliances that off-load the CPU- (Central Processing Unit)-intensive encryption and decryption associated with SSL from the servers. When a server is running SSL by itself, a majority of the available CPUs are consumed with just the cryptographic functions, leaving few resources for actual server functions. With an SSL accelerator, the encryption functionality is off-loaded, and the server is free to do its business unencumbered.
Marriage of Convenience
The main benefit of combining load balancers and SSL accelerators is circumventing a bug in certain versions of Microsoft Windows and Internet Explorer. The bug affects the ability of the load balancer to differentiate between users and keep a particular user directed to a specific Web server. This feature is important for just about any site that involves users logging in, such as an e-commerce site with a shopping cart or a site that generates unique content based on the individual user. These applications are often called "stateful." Because of this, users need to have all their traffic directed to a single individual server for the entirety of their session in a process known as "persistence." For this to occur, the load balancers need to be able to differentiate between various users.
There are several methods available for load balancers to perform this identification: source IP (Internet Protocol) address, session cookie, and SSL session ID. The source IP address is no longer a viable way to separate users because of service providers like AOL, whose millions of customers appear to come from a small number of IP addresses. Cookie-based persistence, in which a load balancer reads a session cookie to distinguish between users, is the method of choice for most sites because it is not affected by large providers the same way that source IP addresses are; however, cookie-based persistence does not work with SSL, because the cookie is encrypted and therefore unreadable. For SSL traffic, the only reliable method for persistence was, at one time, SSL session ID.
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