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The ‘Slashdot effect’

It’s an experience common online – someone sends you a link via email or Twitter or Facebook, perhaps to the newest social networking tool, to an interesting news story, or a photo of a cute kitten. You click on the link and… nothing. Whatever the link is, it’s been too popular for its own good and can’t handle the heavy traffic.

This was known as the ‘Slashdot effect’, after the technology website where links would appear then almost immediately go down because of the attention. Slashdot’s popularity may have waned, but sites such as Reddit and Digg, or popular tweeters such as Stephen Fry or Ashton Kutcher, can make a website unreachable. What’s actually happening here? The number of visits to a website isn’t really the problem. The problem is concurrency – the number of visitors per second. A good way to imagine the problem is a turnstile at a football stadium. The stadium may be able to hold tens of thousands of people, but only a very limited number can fit through the turnstile at once. Try to fit too many through the turnstile, and the whole system breaks down. When hackers bring down websites in a ‘denial of service’ attack, this amounts to the same thing.

Cloud is often seen as the ‘silver bullet’ to cope with high traffic loads, but sites need to be fully optimised from the ground up with that in mind – adding cloud as an afterthought to cope with traffic often isn’t possible. Businesses need to make sure that their website is optimised, using the right databases and correct programming, to take advantage of Cloud hosting.

More importantly, businesses need to consider what they actually need. Sometimes high loads come unexpectedly, but often they are as a result of planned activity – product launches, events or celebrity endorsements. In these cases, your hosting provider can plan for this extra load – adding capacity as it is needed and scaling it down when it isn’t.

Finally, there is always the option of simply not meeting the load, if it’s unnecessary. For example, a ticket agency, or international corporation may need to be online every second of every day, but a few minutes of downtime may not affect your business too much, and the extra cost may be unjustifiable. In this case, it’s important to fail gracefully – a simple page assuring your audience that you’ll be back soon is better than any error message.

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