NEW YORK — Amazon.com struggled Friday to restore computers used by other major websites such as Reddit as an outage stretched well beyond 24 hours.
Though better known for selling books, DVDs and other consumer goods, Amazon also rents out space on huge computer servers that run many websites and other online services.
The problems began at an Amazon data center near Dulles Airport outside Washington early Thursday. On Friday morning, Amazon's status page said the recovery effort was making progress, but it couldn't say when all affected computers would be restored.
Location-sharing social network Foursquare and HootSuite, which lets users monitor Twitter and other social networks more easily, appeared to have recovered.
Many other companies that use Amazon Web Services, like Netflix and Zynga, which runs Facebook games, were unscathed by the outage. Amazon has at least one other major U.S. data center that stayed up, in California.
It's not uncommon for Internet services to become inaccessible due to technical problems, sometimes for hours or even days. But the outage is notable because Amazon's servers are so commonly used, meaning many sites went down at once.
No one knew for sure how many people were inconvenienced, but the services affected are used by millions.
Amazon Web Services provide "cloud," or utility-style, computing in which customers pay only for the computing power and storage they need, on remote computers.
Seattle-based Amazon has big plans for Amazon Web Services. Although it now makes up just a few percent of the company's revenue, chief executive Jeff Bezos said last year that it could rival Amazon's retail business.
Some people consider cloud computing more reliable than conventional hosting services in which a small company might rent a handful of computers in a data center.
If one of them malfunctions, the failure can take down a website. But "clouds" use vast banks of computers. If one fails, the tasks that it performs, such as running a website or a game, can immediately be taken over by others.
But cloud computing isn't immune to failure, either.
Lydia Leong, an analyst for the tech research firm Gartner, said that judging by details posted by Amazon, a network connection failed Thursday morning, triggering an automatic recovery mechanism that then also failed.
Amazon's computers are divided into groups that are supposed to be independent of each other. If one group fails, others should stay up. And customers are encouraged to spread the computers they rent over several groups to ensure reliable service. But Thursday's problem took out many groups simultaneously.