DynamoDB On-Demand Has a Ceiling — and Flash Sales Find It

On-Demand is marketed as scale-to-anything with zero capacity planning. It isn’t quite that — and a flash sale is exactly the kind of event that finds the gap. Hi everyone 👋 DynamoDB On-Demand is pitched as the effortless auto-scaling option — no need to pre-calculate WCU/RCU. That word “automatic” comes with a fine-print condition that matters a lot the first time you hit it. 😱 The disaster scenario A system runs smoothly at a steady ~1,000 requests/second. At midnight, a flash sale kicks off, and traffic jumps to ~20,000 requests/second within seconds.