“But a customer quite legitimately changing their settings had exposed a bug in a software update issued to customers in mid-May, causing “85% of our network to return errors”, it said.”
The bug sat in Fastly’s network for weeks until one customer flipped a valid setting. Amazon, Reddit and the Guardian went down together. Fastly’s testing never caught it, and the company admits it doesn’t know why yet. One config change at one CDN took out a big piece of the web.