EXPLAINER: What caused Amazon's outage? Will there be more?

Robotic vacuum cleaners wouldn't start. Doorbell cameras stopped watching for package thieves, though some of those deliveries were canceled anyway. Netflix and Disney movies got interrupted and The Associated Press had trouble publishing the news.

A major outage in Amazon’s cloud computing network on Dec. 7 severely disrupted services at a wide range of U.S. companies for hours, raising questions about the vulnerability of the internet and its concentration in the hands of a few firms.

That uncertainty was underscored Wednesday when Amazon reported another outage that, while much shorter and less disruptive that the Dec. 7 problem, still created problems for many of its cloud customers. On a status dashboard for the service, Amazon reported that a power failure in one of its data centers had disrupted customers whose tasks ran on its servers.

Power was restored after about 45 minutes, although the company said some customers continued to experience problems almost 12 hours following the outage. Hardware failures in the affected data center forced some Amazon customers to restart their cloud-based systems entirely.

HOW DID IT HAPPEN?

Amazon has still said nothing about what, exactly, went wrong in the early December outage. The company limited its communications at the time to terse technical explanations on an Amazon Web Services dashboard and a brief statement delivered via spokesperson Richard Rocha that acknowledged the outage had affected Amazon’s own warehouse and delivery operations but said the company was “working to resolve the issue as quickly as possible.” It didn't immediately respond to further questions Wednesday.

The incident at Amazon Web Services mostly affected the eastern U.S., but still impacted everything from airline reservations and auto...