15 min
Facebook Took Itself Off the Internet for 7 Hours — and Couldn't Get Back In
At 15:39 UTC on October 4, 2021, a command was issued to audit Facebook's global backbone network capacity. The command contained an error. Within seconds, it severed all fiber-optic connections between Facebook's data centers worldwide. Facebook, Instagram, WhatsApp, and Messenger went dark simultaneously for 3.5 billion users. Engineers trying to fix the problem discovered they couldn't reach the servers remotely — because the corporate authentication systems also ran on the same disconnected backbone. To get back in, they had to physically drive to a data center in Santa Clara.
users locked out globally: 3.5B
duration of full outage: ~7 hrs
market cap lost on the day: ~$47B
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services affected: 5