The most important part of this article is the concept of back pressure and being able to detect it. It's common in a ton of other engineering disciplines but especially important when designing fault tolerant or load balancing systems at scale.

Basically it is just some type of feedback so that you don't overload subsystems. One of the most common failure modes I see in load balanced systems is when one box goes down the others try to compensate for the additional load. But there is nothing that tells the system overall "hey there is less capacity now because we lost a box". So you overwhelm all the other boxes and then you get this crazy cascade of failures.