Design game matchmaking and waiting queue
Overview
This System Design question evaluates a candidate's ability to design scalable, real-time matchmaking and waiting-queue systems, encompassing architecture, data modeling, distributed coordination, concurrency control, reliability, and trade-offs between match quality and latency.
Roblox
Jul 15, 2025, 12:00 AM
Software Engineer
Technical Screen
System Design
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Design a scalable game matchmaking and waiting-queue system
Context
You are designing the matchmaking system for a large real-time multiplayer game. Players join a waiting queue and are matched into games under constraints such as team size, region, and skill level.
Tasks
- Overall architecture: components, data flow, and interactions from Join Queue to Game Start.
- Data model: entities, required fields, indexes, and storage choices.
- Matchmaking algorithm: queueing model, candidate selection, scoring, and formation of matches.
- Fairness and low wait times: policies and mechanisms to balance match quality vs. latency.
- Timeouts, cancellations, retries: ready-check flow, heartbeats, and requeue logic.
- Constraints: team size, region and latency, skill level, parties; how they are enforced and relaxed.
- High concurrency: sharding strategy, worker assignment, and hot-spot mitigation.
- Reliability: idempotency, failure recovery, backpressure, and observability.
Assume a global player base with multiple regions, multiple game modes (e.g., 1v1, 3v3, 5v5), and peak spikes. Target low wait times and high match quality.
Solution
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