Retry amplification and metastable failure

The multiplication

Retries compose multiplicatively down a call chain:

client -> gateway -> service -> database
  3x   x    3x    x    3x    =  27x load at the database

The amplification arrives exactly when the database is least able to serve it. A dependency 20% degraded now receives 27x traffic. This is the standard route from a blip to an outage.

Metastable failure

A system is in a metastable failure state when it stays down after the original trigger is gone, because the failure now sustains itself.