In October, problems with the same Amazon data center in Virginia took down Reddit, Foursquare and Heroku. The instance was explained on the status Web site as “degraded performance” in some parts of Amazon’s storage service. In June, a lightning storm hit the Virginia data center, taking Netflix as well as Pinterest, Instagram and other sites off line for hours. That time, too, customers were offered little insight into what had happened.

In April 2011, an Amazon failure took down many smaller sites that had rented cloud storage space from the Internet giant. That time, the companies that were most affected were start-ups that were less likely to pay for so-called redundancies, or backup systems that kick in when a service fails. Netflix was not affected then, and said at the time it was because it had taken advantage of the redundancies that Amazon offers.

Netflix has said that it has built several redundancies into its cloud-based system. For instance, it stores its data across multiple “zones,” so if there is a failure in one zone, it can retry in another. It says it also spends money on more capacity than it needs, so that if there are large spikes in customer activity, the service is less likely to go down.

Joris Evers, a Netflix spokesman, declined to elaborate on why Netflix went down despite these safeguards. He said the company was investigating the cause and would do what it could to prevent the interruption from recurring.

“We are happy that people opening gifts of Netflix or Netflix-capable devices on Christmas morning could watch TV shows and movies and apologize for any inconvenience caused Christmas Eve,” Mr. Evers said.