Amazon.com Inc. apologized Friday for a data-center outage that brought down major websites including Foursquare and Reddit and offered Web services customers a 10-day credit.

The company isn't disclosing how much the credit will cost it. Amazon Web Services accounts for only a few percent of Amazon's total revenue, but the company has high hopes for the business. The service rents out computer time by the hour.

The outage at the data center near Dulles Airport, outside Washington, was a major stumble for the service. Amazon is still restoring some of the computers brought down in the incident, which began eight days ago.

In a post-mortem report Friday, Seattle-based Amazon said human error set off the outage. An automated error-recovery mechanism then went out of control, and many computers became "stuck" in recovery mode.

The service is set up in a way that's supposed to provide redundancy, by letting computers in a different "availability zone" take over when one fails. Amazon said that customers that were properly set up to run their computing tasks over multiple zones were largely unaffected, but that the error made it difficult to switch zones on the fly. It's making changes to prevent the error from recurring.

The credit applies to all customers using the zone that went down, whether they were directly affected or not. Amazon has not revealed how many customers were affected.

Amazon shares rose 45 cents to $195.52 in morning trading Friday.