TL;DR: Every booking goes through one Redis Lua script. The script checks, in order, whether the candidate is already admitted, whether their level is full, and whether any seat is left overall. Then it counts the seat and marks the candidate.

Source: [Dev.to](https://dev.to/sumonselim/designing-a-flash-sale-seat-reservation-system-in-aws-part-2-never-sell-a-seat-twice-4j61)

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