Overview
Chaos Monkey was the first tool in Netflix's 'Simian Army.' It is based on the idea that the best way to ensure a system can handle failures is to cause them frequently and automatically, forcing engineers to build fault-tolerant architectures.
How it Works
Chaos Monkey runs as a service that periodically selects a random virtual machine instance and shuts it down. If the system is well-designed, the loss of a single instance should have no impact on the overall service.
Importance
Chaos Monkey popularized the discipline of Chaos Engineering, moving it from a niche practice to a mainstream DevOps strategy for building highly available systems.