14 DAY TRIAL // Twitter was unavailable or available intermittently for several hours yesterday. Heavy Twitter users, understandably, were in shock. People complained and they didn't know what to do. Twitter acknowledged the problem as it happened and provided some updates, but was mostly quiet until after the issue was fixed.
There are plenty of theories regarding the outage, from hacking attacks to GIF avatars (really), but in the end it was all caused by a mundane "cascading bug," i.e. one that propagated itself over Twitter's infrastructure, a term that quickly got its very own parody account.
"At approximately 9:00am PDT, we discovered that Twitter was inaccessible for all web users, and mobile clients were not showing new Tweets," Twitter explained.
"We immediately began to investigate the issue and found that there was a cascading bug in one of our infrastructure components," it said.
"A 'cascading bug' is a bug with an effect that isn’t confined to a particular software element, but rather its effect 'cascades' into other elements as well. One of the characteristics of such a bug is that it can have a significant impact on all users, worldwide, which was the case today," Twitter explained.
Twitter eventually had to roll back to a previous stable version of the site, which indicates that the bug was introduced during an update. This is how most outages start out. But sites like Twitter are always updated, with new features, improvements or tweaks and it goes smooth most of the time.
The big takeaway from this is the fact that so many people were actually surprised by this. People forget so easily, Twitter has been rock stable for the past couple of years, but that wasn't always the case. In fact, not so long ago, an outage like this would have been a common occurrence, people wouldn't even have noticed it.
"For the past six months, we’ve enjoyed our highest marks for site reliability and stability ever: at least 99.96% and often 99.99%. In simpler terms, this means that in an average 24-hour period, twitter.com has been stable and available to everyone for roughly 23 hours, 59 minutes and 40-ish seconds. Not today though," Twitter explained. That's not something that anyone would imagine Twitter saying, three or four years ago.