engineering-redis-game-patterns

Redis Game Patterns

Purpose

Redis usage patterns for games — leaderboards, session caching, pub/sub messaging, rate limiting, ephemeral state, and sorted sets for real-time game data.

When to Use

Trigger: Redis, pub/sub, leaderboard, session cache, rate limiting, sorted sets, game cache, ephemeral state, TTL, player presence, cross-server messaging

Prerequisites

None — this is a foundational infrastructure skill.

Core Principles

Will Wright: "Simulation state must be fast, ephemeral, and disposable — persistence is for outcomes, not for process."

Redis is for hot data, PostgreSQL is for cold data — cache what's accessed frequently, persist what matters long-term
Every cached value needs a TTL — stale data is worse than no data; always set expiration
Use the right data structure — sorted sets for leaderboards, hashes for sessions, pub/sub for events, strings for simple counters
Cache-aside pattern by default — check cache, miss, load from DB, populate cache; never assume cache is populated
Atomic operations prevent race conditions — use pipelines and Lua scripts for multi-step operations, never read-then-write
Separate Redis connections for pub/sub — subscriber connections are blocked; use dedicated connections for subscriptions
Namespace all keys — prefix keys by domain (lb:, session:, rl:, presence:) to avoid collisions and enable selective flushing

Step-by-Step Instructions

1. Install Dependencies

bun add ioredis

2. Configure Redis Connection

Use boilerplate/redis-client.ts for the base connection with reconnection logic and error handling. All other modules import from this file.

3. Set Up Leaderboards

Use boilerplate/leaderboard.ts for sorted-set-based leaderboards. Supports adding scores, fetching top N, getting player rank, and fetching nearby ranks. Includes periodic snapshot to PostgreSQL for historical data.

4. Implement Session Caching

Use boilerplate/session-cache.ts for player session caching with TTL. Follows cache-aside pattern: check cache → miss → load from DB → populate cache.

5. Configure Pub/Sub

Use boilerplate/pub-sub.ts for cross-server messaging. Requires separate Redis connections for publishing and subscribing. Typed event handlers ensure type safety.

6. Add Rate Limiting

Use templates/rate-limiter.ts for per-player per-action sliding window rate limiting using sorted sets. Configurable window size and max requests.

7. Manage Ephemeral State

Use templates/ephemeral-state.ts for short-lived game state: match state with TTL, player presence via heartbeat, and temporary buffs/effects.

Code Examples

Adding a player score to a leaderboard

import { leaderboard } from './leaderboard';

await leaderboard.addScore('weekly', 'player_123', 4500);
const top10 = await leaderboard.getTopN('weekly', 10);
const rank = await leaderboard.getPlayerRank('weekly', 'player_123');

Caching a player session

import { sessionCache } from './session-cache';

const session = await sessionCache.get('player_123');
if (!session) {
  const fromDb = await db.query.players.findFirst({ where: eq(players.id, 'player_123') });
  await sessionCache.set('player_123', fromDb, 3600);
}

Publishing a game event across servers

import { publisher, subscriber } from './pub-sub';

await publisher.publish('match-events', {
  type: 'match-started',
  matchId: 'match_456',
  players: ['player_123', 'player_789'],
});

subscriber.on('match-events', (event) => {
  console.log('Match event:', event.type);
});

Rate limiting a player action

import { checkRateLimit } from './rate-limiter';

const result = await checkRateLimit('player_123', 'attack', {
  maxRequests: 1,
  windowSeconds: 5,
});

if (!result.allowed) {
  throw new Error(`Rate limited. Retry after ${result.retryAfter}s`);
}

See boilerplate/ for full implementations and templates/ for rate limiting and ephemeral state patterns.

Cross-References

game-backend-architecture for integrating Redis into the game server
bullmq-game-queues for job queues built on Redis
postgres-game-schema for persisting leaderboard snapshots and session fallback data

Pitfalls & Anti-Patterns

Don't use Redis as a primary database — Redis is a cache and message broker; always have a persistence layer backing it
Don't forget TTLs — keys without expiration accumulate forever and eventually exhaust memory
Don't use KEYS * in production — it blocks Redis; use SCAN for key enumeration
Don't share a single connection for pub/sub and commands — subscriber connections are blocked and cannot execute other commands
Don't store large objects in Redis — keep values small (< 1MB); store IDs and fetch details from the database
Don't assume cache is populated — always implement cache-aside; never trust that a key exists

Designer Philosophy

Will Wright (SimCity, The Sims): Simulation state management is about speed and disposability. In SimCity, the game constantly recalculates traffic, power, and zoning — none of that intermediate state needs to survive a restart. Redis serves this exact role in multiplayer games: it holds the hot, fast-changing state that drives the simulation, while the database records outcomes that matter. The moment you treat cache as truth, you've confused process with product.

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