Requirements

Functional Requirements:

• Matchmaking pairs players by skill level based on ELO rating.
• Provide real-time move updates between players via persistent connection (WebSocket).
• Enforce chess rules with server-side move validation, rejecting invalid moves.
• Store completed games and allow users to review past games and replay moves.
• Maintain user accounts with profiles, ELO ratings, win/loss records, and game statistics.

Non-Functional Requirements:

• Availability - 99.99% uptime
• performance: service needs to have p99 of under 200ms for realtime gameplay. Gameplay performance > historical gameplay
• Scalability - 10 DAU and 1 million peak concurrent users
• consistency & correctness- realtime game play very important!
• Game integrity - server validated game play with feedback
• fault tolerance: This system should withstand fault tolerance

API Design

I will REST and websocket API calls

POST/v1/matchmaker

{

"ELO_rating": {elo_rating}

"user_id": "frodo"

}

response

{

"status": "queued"

"queue_id": {queue_id}

}

Websocket is already open at time of app load

server pushes result via websocket

{

"status": "matched"

"opponent_id": "gandalf"

"game_id": {gameid}

"match_id": {matchid}

"myboardside": "black"

:oppboardside": "white"

"opp_elo_rating": {rating}

"gameid": {gameid}

"createdat": {unixtime}

}

user123 -> websocket connection

GET/v1/games/{gameid}

GET/v1/user/{userid}/games

Websocket connection at appload

WSS://url.ingameservice.com/ws

High-Level Design

Detailed Component Design

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.