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Always On

This Internet is never supposed to sleep. Banks advertise Web banking 24 hours a day, 7 days a week. This 24x7 mentality is part of what makes the Internet so enticing for users. People naturally assume that, at any time, it exists as an available resource. However nice this feature is for users, it is equally daunting for Web application designers. A good example of what can happen when an application is not available 24x7 is the trouble users had with eBay, the online auctioneer, in late 1999 and 2000.

During various system or software upgrades over that time, eBay suffered intermittent problems that made it unavailable to users. In June of 1999, it was unavailable for 22 hours. Since the purpose of eBay's service is to manage millions of time-limited auctions, its core business was directly affected. Instead of selling to the highest bidder, some sellers were forced to sell to the "only bidder." Users complained, demanding a reduction in fees. The problems made the news, and the company was forced to issue apologies in addition to refunding some fees. This is not to say that eBay is not a scalable service or that the system is always unstable; indeed, eBay is one of the most trafficked sites on the Internet, and except in rare instances, has done a tremendous amount of successful 24x7 processing.

However, this simple example does underscore the importance of 24x7 when it comes to Web applications. Nobody will write news stories about how well you perform 24x7 service, but they will definitely take you to task for glitches when you don't. These problems can affect your whole company, especially if part of its revenue comes via the Web.

Observant readers might argue that failure to provide 24x7 service is not a question of scalability but of reliability. True, the inability to provide service because of a system failure is a question of reliability and robustness. From the practical standpoint of the user, however, it does not matter. Whether the application is unavailable because of a power problem with the site's Internet service provider (as was the case in one of eBay's outages) or because the system can't handle a million simultaneous users, the result is the same: The application is unavailable.

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