Multiplayer Game Backend
Hold a 50ms tick budget through launch day.
Hold a ~50ms tick budget through launch day while instances die and a zone link severs.
Every player action must round-trip inside the tick budget, so the sim fleet and its stores live or die by headroom. Session state sits in a KV; matchmaking and profile reads must come from a cache — a store round-trip per tick blows the budget, and a lost sim instance must hand its matches to survivors.
Components in play
- Realtime gateway — Holds player connections and routes actions to the sim fleet.
- Game-sim fleet — Runs the authoritative tick loop for live matches.
- Sim-write fan-out — Splits sim-fleet output between the session KV write path and the match/profile cache reads so neither branch starves.
- Match/profile cache — Serves matchmaking and profile reads without touching the store.
- Session-state KV — Snapshots of live sessions so a match survives its instance.
Graded on these SLOs
- ≥ 99.00%Actions land
- ≤ 50 msTick-budget p99
- ≥ 12k rpsSustain the actions
- ≤ 90%Fleet headroom
- ≤ 10Lean fleet
The brief
Design the backend behind a live multiplayer game: players connect, take actions, and every action has to round-trip inside a tight tick budget for the game to feel real. Session state has to survive a crashed instance, matchmaking and profile reads can't touch the hot path, and a launch-day login stampede can't be allowed to blow the budget.
Functional
- Run the authoritative simulation for live matches
- Persist session state so a match survives its instance
- Serve matchmaking and profile lookups
Non-functional
- Action-to-fill latency stays inside the tick budget (~50ms p99)
- A crashed sim instance doesn't drop the matches it was running
- Survive a launch-day login stampede without degrading the tick
Warm-up: design decisions
Optional theory to prime the calls a senior engineer would make before you build.
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