Amazon Cloud Failure Takes Down Web Sites

A widespread failure in Amazon’s Web services business took down many Internet sites on April 21, highlighting the risks involved when companies rely on so-called cloud computing.

The problems, which began early Thursday morning and had not been completely repaired by the end of the day, affected sites including Quora.com, Reddit.com, GroupMe.com and Scvngr.com, which all posted messages to their visitors about the issue. Most of the sites were inaccessible for hours, and others were only partly operational. The Web companies use Amazon’s cloud-based service to serve their Web sites, applications and files. Amazon’s customers include start-ups like the social networking site Foursquare but also big companies like Pfizer and Nasdaq. Amazon, which is a leader in this business, lets these companies rent space on its servers and take advantage of its big data centers and computing power. But that gives the companies little control if the servers fail.