Amazon explains its cloud disaster

By David Goldman, staff writer


NEW YORK (CNNMoney) -- Amazon on Friday issued a detailed analysis and apology on last week's massive crash of its cloud service, an event that brought down dozens of websites.

The disruption to Amazon (AMZN, Fortune 500) Web Service's Elastic Compute Cloud, or EC2, limited customers' access to much of the information that was stored in the company's East Coast regional data centers. About 75 sites crashed because of the outage.

Until now, Amazon had stayed relatively silent about the cause. But after completing a post-mortem assessment of the mess, the company issued a technically detailed, 5,700-word explanation of what went wrong.

The event -- the first prolonged, widespread outage EC2 has suffered since launching five years ago -- was a technical perfect storm. A mistake made by Amazon's engineers triggered a cascade of other bugs and glitches.

"As with any complicated operational issue, this one was caused by several root causes interacting with one another," Amazon wrote.

On April 21, AWS tried to upgrade capacity in one storage section of its regional network in Northern Virginia. That section is called an "availability zone." There are multiple availability zones in each region, with information spread across several zones in order to protect against data loss or downtime.

The upgrade required some traffic to be rerouted. Instead of redirecting the traffic within its primary network, Amazon accidentally sent it to a backup network. That secondary network isn't designed to handle that massive traffic flood. It got overwhelmed and clogged up, cutting a bunch of storage nodes off from the network.

When Amazon fixed the traffic flow, a failsafe triggered: The storage volumes essentially freaked out and began searching for a place to back up their data. That kicked off a "re-mirroring storm," filling up all the available storage space. When storage volumes couldn't find any way to back themselves up, they got "stuck." At the problem's peak, about 13% of the availability zone's volumes were stuck.

But why did a problem in one availability zone ripple out to affect a whole region? That's precisely the kind of glitch Amazon's infrastructure is supposed to prevent.

Turns out EC2 had a few bugs. Amazon describes them in detail in its analysis, but the gist is that the master system that coordinates all communication within the region had design flaws. It got overwhelmed, suffered a "brown out," and turned an isolated problem into a widespread one.

Interestingly, those bugs and design flaws have always been in place -- but they wouldn't have been discovered if Amazon hadn't goofed up and set off a domino chain.

Amazon says that knowing about and repairing those weaknesses will make EC2 even stronger. The company has already made several fixes and adjustments, and plans to deploy additional ones over the next few weeks. The mistake presented "many opportunities to protect the service against any similar event reoccurring," Amazon said.

Of course, Amazon's customers aren't so thrilled to have been guinea pigs in this cloud-crash learning experience. Amazon offered a mea culpa, and said it would give all customers in the affected availability zone a credit for 10 days of free service.

"We want to apologize," the company said in a prepared statement. "We know how critical our services are to our customers' businesses and we will do everything we can to learn from this event and use it to drive improvement across our services." To top of page

Frontline troops push for solar energy
The U.S. Marines are testing renewable energy technologies like solar to reduce costs and casualties associated with fossil fuels. Play
25 Best Places to find rich singles
Looking for Mr. or Ms. Moneybags? Hunt down the perfect mate in these wealthy cities, which are brimming with unattached professionals. More
Fun festivals: Twins to mustard to pirates!
You'll see double in Twinsburg, Ohio, and Ketchup lovers should beware in Middleton, WI. Here's some of the best and strangest town festivals. Play
Index Last Change % Change
Dow 16,912.11 -70.48 -0.42%
Nasdaq 4,442.70 -2.21 -0.05%
S&P 500 1,969.95 -8.96 -0.45%
Treasuries 2.46 -0.03 -1.16%
Data as of 7:36am ET
Company Price Change % Change
Frontier Communicati... 6.79 0.85 14.31%
Windstream Holdings ... 11.83 1.30 12.35%
AT&T Inc 36.59 0.94 2.64%
CenturyLink Inc 39.90 2.19 5.81%
Bank of America Corp... 15.34 -0.16 -1.03%
Data as of Jul 29

Sections

McDonald's in Japan says profit and sales will fall short of expected targets this year, as fallout widens over a major food safety scandal. More

Amgen is the latest to continue corporate America's cost cutting strategy, even as the economy is supposedly on the mend More

Bunch o Balloons allows multiple water balloons to be filled at once. Parents are loving it -- to the tune of $645,000. More

Steve Mason, a pastor from California, inherited more than $100,000 in student loan debt when his 27-year-old daughter died suddenly in 2009. With interest and late penalties, the debt has since ballooned to $200,000. More

Market indexes are shown in real time, except for the DJIA, which is delayed by two minutes. All times are ET. Disclaimer Morningstar: © 2014 Morningstar, Inc. All Rights Reserved. Disclaimer The Dow Jones IndexesSM are proprietary to and distributed by Dow Jones & Company, Inc. and have been licensed for use. All content of the Dow Jones IndexesSM © 2014 is proprietary to Dow Jones & Company, Inc. Chicago Mercantile Association. The market data is the property of Chicago Mercantile Exchange Inc. and its licensors. All rights reserved. FactSet Research Systems Inc. 2014. All rights reserved. Most stock quote data provided by BATS.