Online Multiplayer Game Server — Simple

Problem statement (interviewer prompt)

Design the server for a fast-paced multiplayer game (FPS / battle royale): handle 100+ player matches, deterministic state replication at 60Hz, client-side prediction + server reconciliation, lag compensation, anti-cheat, and matchmaking at 1M+ concurrent players.

flowchart LR
  P1[Player 1]
  P2[Player 2]
  AUTH[Auth + Lobby]
  GS[Game Server<br/>authoritative state]
  P1 --> AUTH
  P1 --> GS
  P2 --> AUTH
  P2 --> GS
  GS --> P1
  GS --> P2

    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 P1,P2,AUTH,GS service;