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Why Amazon crashed on Prime Day and how it responded

The company couldn't handle the surge in traffic during its biggest shopping event, according to internal documents seen by CNBC.

Prime Day
Amazon hustled to fix glitches on Prime Day.
Getty Images

We may have answers as to why Amazon suffered glitches at the start of Prime Day on Monday. 

The e-commerce giant didn't have enough servers to handle all the traffic on its site during one of its biggest sales days of the year, according to internal documents obtained by CNBC. That led the company to launch a simpler backup front page and temporarily block international traffic. 

This reportedly happened 15 minutes after Prime Day -- a 36-hour sale featuring more than 1 million deals -- kicked off at noon PT on Monday. 

 Amazon reportedly had to manually add servers to try to keep up with the traffic surge. Experts who reviewed the documents told CNBC this indicated the company's auto-scaling feature might not have been working leading up to the crash. About an hour after Prime Day kicked off, an update on the status of Amazon's servers said, "Currently out of capacity for scaling. Looking at scavenging hardware."

A breakdown in Sable, Amazon's internal computation and storage system, reportedly led to glitches across Prime, authentication and video playback. A status update a little after 1 p.m. PT gave Sable a "red" emergency alert and said it was "running hot" and "cannot scale," according to CNBC.

"We are experiencing failures mostly related to Sable," an update reportedly said.

Alexa, Prime Now and Twitch also experienced issues on Prime Day. Some warehouses reportedly couldn't scan products or pack orders for a while. 

Even after putting up a scaled-down "fallback" front page and restricting international traffic, the Amazon site's "error rate" reportedly got worse until around 1:05 p.m. PT and improved drastically at 1:10 p.m. PT. A person familiar with the matter told CNBC that the office was "chaotic," with more than 300 people joining an emergency conference call at one point. 

Jeff Wilke, Amazon's CEO of worldwide retail, said in an internal email seen by CNBC that his team was "disappointed" about the glitches, and that the company's working to make sure it doesn't happen again. 

Amazon didn't immediately respond to a request for comment. 

Despite the glitches, Amazon said this year's Prime Day was "the biggest shopping event in Amazon history," with customers ordering more than 100 million products in 36 hours.

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