Developer Builds Concurrency-Safe Movie Seat Reservation System Using FastAPI and Redis

A developer built a movie reservation backend to explore how production systems prevent double-bookings when multiple users attempt to reserve the same seat simultaneously. The project uses FastAPI, PostgreSQL, Redis, and SQLAlchemy, organized in a layered architecture separating controllers, business logic, and database operations. Redis temporary locks prevent simultaneous seat selection, while Lua scripts ensure that multi-seat reservations are acquired atomically — either all seats are locked or none are. Lock ownership verification adds another safeguard, ensuring expired locks cannot be exploited by stale reservation requests. PostgreSQL unique constraints serve as a final failsafe, making duplicate seat bookings impossible even if all application-level protections fail.