I wanted to write an upbeat article to congratulate Office 365 on delivering a successful six months of flawless service since their last major outage on September 8/9 2011. Although six months is nothing really to boast about in an era when Service Level Agreements (SLAs) call for delivery of well over 99.9% availability, I think it’s still important to acknowledge progress and say that Office 365 now exhibits signs of a mature and reliable service in which customers can have confidence. And then my confidence was shattered by the Microsoft Azure outage (or rather, a service disruption) that was apparently caused by a software problem dealing with leap years. As Bill Laing, Corporate VP for Server and Cloud, reported, the problem appeared to be due to a “time calculation that was incorrect for the leap year”. Of course, leap years only occur every four years and February 29 2012 was the first time that a Microsoft cloud service woke up to find that February and 29 was now part of its reality, but wouldn’t you have thought that someone like a software architect might have taken leap years into account when Microsoft designed the service?
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