Hystrix (https://github.com/Netflix/Hystrix) is a latency and fault tolerance library designed to isolate points of access to remote systems, services, and third-party libraries. It can stop cascading failures and enable resilience in complex distributed systems where failure is inevitable.

Hystrix is designed to do the following:

• Stop cascading failures in a complex distributed system
• Protect the system from the failures of dependencies over the network
• Control the latency of the system
• Recover rapidly and fail faster to prevent cascading
• Fall back and gracefully degrade when possible
• Enable near-real-time monitoring, alerting, and operational control

When you have an application in a complex distributed architecture with a lot of dependencies, some of these dependencies will inevitably fail at some point. If your application is not isolated from these external failures, there is the risk of the application going down along with the dependency.  

Hystrix is currently in maintenance mode and future versions of JHipster might migrate to a different library for fault-tolerance and circuit-breaking.