On Monday night, Facebook had its biggest outage ever, with WhatsApp, Instagram, Messenger, and even Facebook's internal tools all being unavailable for almost six hours.
Simply defined, it was due to the internet protocol that converts words like Facebook.com into a language that computers understand.
DNS converts our data and directs us to the services and apps we requested. When this service is down, the services appear to be down, but they are just unavailable.
For clarity, here's what happened - Facebook accidentally sent an update to the routing protocol stating - hey, we do not have our servers anymore at this destination.
While, this should be pretty easy to fix, since all one needs to do is, send a request once again - hey, our servers are located here.
But since Facebook runs everything through Facebook, they were locked out of sending the message and the building that contains the data servers that can be used to send the message.
The company later found a way back in, made the necessary changes, and boom the services were back to being normal.