A surprising portion of the web went dark on Saturday thanks to a major storm which knocked out much of Amazon's Elastic Compute Cloud. Clients of Amazon's EC2 include the likes of Netflix, Instagram and Pinterest – all of which went dark on Saturday. Of course, this is not the first time Amazon's web services have been rendered helpless by intense storms. Believe it or not, Amazon's servers account for nearly 1 percent of the Internet.
However, it wasn't just Amazon's data centers wreaking havoc upon online service availability. As it turns out, a number of websites fell prey to a leap second bug which also caused disruptions. Amongst the sites affected by the bug were Gawker (Parent of Lifehacker, Gizmodo and others), Reddit, Mozilla and most likely many others.
Every so often, International timekeepers add one second to global time standards in order to offset differences between our ultra-precise atomic clocks and the natural rotation of the planet – a rotation which is ever so slightly irregular. Because the spin of our blue marble isn't as exact as the oscillation of atoms, these tiny time adjustments are performend whenever they are needed and not necessarily done at fixed, periodic intervals. The last change was made in 2008.
The new and improved time eventually propagates via NTP (Network Time Protocol) to many computers across the world. Many web servers, too, are configured for NTP as well. Somehow though, some software isn't able to handle this unexpected change in seconds and the result is what we saw on Saturday.
Hours, minutes, seconds – these are all man-made constructs with measurably precise definitions. However, the rotation and orbit of the Earth are actually less perfect than human standards and the instruments we use to measure them.
Even though the differences between atomic clock read outs and Earth's ballerina-like spin may be too miniscule for you and I to notice, the difference adds up. In fact, it adds up enough to offset human time from planetary time by minutes – even hours – over the course of many years. For this reason, we continue to make adjustments in order to ensure morning, noon and night line up with what we've come to expect.