When One Slow Service Took Down an Entire Region: The Circuit Breaker Pattern Explained
On September 20, 2015, Amazon DynamoDB in US-East-1 went dark for over four hours. The root cause wasn’t a hardware failure or a cyberattack—it was a feedback loop. Storage servers couldn’t retrieve their partition assignments from a metadata service, so they retried. The metadata service became overwhelmed. More timeouts. More retries. More overload. Engineers eventually had to firewall the metadata service from storage servers entirely, effectively taking DynamoDB offline to break the cycle. ...