How Poor API Design With No Rate Limiting Caused a $10M Cloud Outage

A 2021 incident at a major cloud provider resulted in an estimated $10 million revenue loss after a single internal API with no rate limiting triggered a cascading failure. A misconfigured service entered a retry loop generating 10,000 requests per second, bringing the API down within minutes and taking three dependent services offline. Customers were locked out of their data for four hours before engineers traced the root cause. The outage highlighted critical gaps in API design, including the absence of rate limiting, circuit breakers, and retry guidance headers. Proper REST API design — covering correct HTTP method usage, status codes, rate limiting strategies like token buckets and sliding windows, JWT authentication, and security best practices — can prevent such failures at scale.