HLD11 min read

Design a Multiplayer Game Server (FPS / battle royale)

Authoritative game server: tick-based simulation, lockstep / client-prediction, regional matchmaking, anti-cheat, and ~100 ms p95 round-trip.

hldsystem-designreal-timegaming

Intro

A real-time multiplayer game server (Fortnite, COD Warzone, Valorant) runs an authoritative simulation at 60 Hz tick rate per match. Players send inputs, the server simulates and broadcasts state, clients render with prediction + reconciliation. The hard parts are sub-100 ms RTT to all players in a match, anti-cheat, regional matchmaking, and the ops complexity of running thousands of stateful servers.

Functional

Matchmaking — group N players into a match by skill + region.
Authoritative server simulates the game at 60 Hz.
Receive inputs + broadcast state with prediction / reconciliation.
Persist results — XP, stats, leaderboards.

Non-functional

Round-trip p95 < 100 ms (regional).
60 Hz tick = 16.67 ms simulation budget per tick.
100 k concurrent matches × ~50 players = 5 M concurrent players.
Anti-cheat — server is authoritative; client-side detection complementary.

Components

Matchmaker
Skill + region grouping; emits match assignments.
Game server fleet
Per-match dedicated server (UDP).
Session orchestrator
Spins up game servers (Kubernetes / Agones).
State broadcaster
60 Hz delta updates over UDP to clients.
Anti-cheat
Server-side validation + client kernel module (BattlEye / EAC).
Persistence
Leaderboards, XP, match history.

Trade-offs

Authoritative server vs lockstep

Pros

Authoritative: anti-cheat-friendly, smaller messages.
Lockstep: deterministic; lower bandwidth.

Cons

Authoritative: server CPU.
Lockstep: any desync = game over.

TCP vs UDP for state sync