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How a Tiny React Bug Triggered a Thundering Herd: Lessons from Cloudflare’s Sept 12 Outage
On September 12, 2025, a small bug in Cloudflare’s Dashboard code (a React useEffect dependency mis-configuration) triggered a Thundering Herd Problem that brought down its Tenant Service API and disrupted multiple services. Learn how it happened, what mitigations worked, and how you can prevent similar failures in your systems.