Clinic Appointment Booking

A healthcare company operates thousands of clinics, and patients book appointments through a mobile application. The system has a hard concurrency problem: two patients may try to book the final available slot at exactly the same moment, and only one booking can succeed. Traffic is ordinary for most of the day but becomes extreme when appointments for popular doctors are released. The company wants a serverless architecture and does not want to manage database servers. Appointment data must remain durable and the system should scale automatically.