Ticketmaster / BookMyShow — Simple

Problem statement (interviewer prompt)

Design Ticketmaster / BookMyShow: users browse events, see a seat map, hold a seat for ~7 minutes while paying, then receive a ticket. Guarantee no double-booking even during 500k-concurrent-user drops for hot shows. Add anti-bot defences.

flowchart LR
  U([User])
  CAT[Event Catalog]
  SEAT[Seat Map Service]
  HOLD[Seat Hold<br/>TTL lock]
  PAY[Payment]
  TKT[Ticket Issue]
  U --> CAT
  U --> SEAT
  SEAT --> HOLD
  HOLD --> PAY --> TKT

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class U client;
    class CAT,SEAT,HOLD,PAY,TKT service;