The sites that could not be reached also included some Amazon pages, the Financial Times, Reddit, Twitch and The Guardian.

San Francisco-based Fastly acknowledged a problem just before 6 a.m. Eastern. About an hour later, the company said: "The issue has been identified and a fix has been applied." Most of the sites soon appeared to be back online.

The company said in an emailed statement that it was a "technical issue" and "not related to a cyber attack."

Still, major futures markets in the U.S. dipped sharply minutes after the outage, which came a month after hackers forced the shutdown of the biggest fuel pipeline in the U.S.

Fastly is a content-delivery network, or CDN. It provides vital but behind-the-scenes cloud computing "edge servers" to many of the web's popular sites. These servers store, or "cache," content such as images and video in places around the world so that it is closer to users, allowing them to fetch it more quickly and smoothly.