This is the worst outage we’ve had in over four years, and we wanted to first of all apologize for it.
Facebook went to outage for about two and half hours on Thursday. According to Robert Johnson of Facebook, The key flaw that caused this outage to be so severe was an unfortunate handling of an error condition. An automated system for verifying configuration values ended up causing much more damage than it fixed.
To address the problem, the site temporarily turned off by Facebook to stop all transactions to the database in which "Facebook DNS Error" showed to the Facebook.
The way to stop the feedback cycle was quite painful - we had to stop all traffic to this database cluster, which meant turning off the site. Once the databases had recovered and the root cause had been fixed, we slowly allowed more people back onto the site.
What is DNS? DNS or Domain name system is a naming system designed to simplify and designate a human-friendly name of the address designated to a certain web address. For instance, Facebook.com here in my area is accessible at http://18.104.22.168/, instead of accessing it through that address or remembering that block of numbers each time I visit the site, I would simply type Facebook.com to my browser.
When does DNS Error happens? DNS error happens when for example Facebook which is supposedly accessible to a given address was made or accidentally made inaccessible. A simpler example is, I turned off my computer or it's busted which is supposedly accessible to a certain ip address mapped onto it.