Facebook—and apparently all the major services Facebook owns—are down today. We first noticed the problem at about 11:30 am Eastern time, when some Facebook links stopped working. Investigating a bit further showed major DNS failures at Facebook:
So, @facebook‘s DNS is broken this morning…
— Jim Salter (@jrssnet) October 4, 2021
DNS—short for Domain Name System—is the service which translates human-readable hostnames (like arstechnica.com) to raw, numeric IP addresses (like 18.104.22.168). Without working DNS, your computer doesn’t know how to get to the servers that host the website you’re looking for.
The problem goes deeper than Facebook’s obvious DNS failures, though. Facebook-owned Instagram was also down, and its DNS services—which are hosted on Amazon rather than being internal to Facebook’s own network—were functional. Instagram and WhatsApp were reachable but showed HTTP 503 (no server is available for the request) failures instead, an indication that while DNS worked and the services’ load balancers were reachable, the application servers that should be feeding the load balancers were not.
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