Latency Monkey

Latency Monkey is a member of the Simian Army that introduces artificial network delay and packet loss into Netflix's production infrastructure to test how services behave under degraded network conditions. Where Chaos Monkey tests availability by terminating instances, Latency Monkey tests performance isolation by slowing down the communication between services.

The tool is designed to verify that timeout logic, circuit breakers, and fallback mechanisms actually function when network latency exceeds expected thresholds. Many distributed systems are designed with optimistic assumptions about network speed; Latency Monkey makes those assumptions explicit by violating them. A service that fails when latency increases by 100 milliseconds has a latent dependency on network quality that would eventually cause an outage during a real degradation.

Latency Monkey exemplifies a principle from control theory: a system cannot be considered stable until it has been tested against the full range of disturbances it might encounter. Network latency is not an exception to normal operation. It IS normal operation, at least some of the time.