Redis — Caching, Sessions & Beyond

What is Redis?

Redis is an in-memory data store — a supercharged shared Map that your entire application cluster can access. It reads/writes in microseconds, supports TTL-based expiration, and persists to disk. The universal tool for: caching, sessions, rate limiting, real-time features, and lightweight queues.

Core Data Types

Using Redis with Node.js (ioredis)

npm install ioredis

import Redis from 'ioredis';
const redis = new Redis(process.env.REDIS_URL); // redis://redis:6379

// Cache-aside pattern
async function getUserById(userId) {
  const key = `user:${userId}`;
  const cached = await redis.get(key);
  if (cached) return JSON.parse(cached);

  const user = await db.users.findById(userId);
  await redis.setex(key, 300, JSON.stringify(user)); // 5 min TTL
  return user;
}

// Invalidate on update
async function updateUser(userId, data) {
  await db.users.update(userId, data);
  await redis.del(`user:${userId}`);
}

// Rate limiting
async function rateLimit(ip, limit=100, window=60) {
  const key = `ratelimit:${ip}`;
  const count = await redis.incr(key);
  if (count === 1) await redis.expire(key, window);
  return count <= limit;
}

// Session storage (connect-redis)
import session from 'express-session';
import { RedisStore } from 'connect-redis';
app.use(session({
  store: new RedisStore({ client: redis }),
  secret: process.env.SESSION_SECRET,
  resave: false, saveUninitialized: false,
  cookie: { secure: true, maxAge: 86400000 }
}));

TTL Management

await redis.setex('key', 300, 'value');   // Set with 300s TTL
const ttl = await redis.ttl('key');        // Time remaining (-1=no expiry, -2=gone)
await redis.expire('key', 600);            // Reset TTL without changing value
await redis.del('key');                    // Delete immediately

Redis Persistence

# docker-compose.yml (enables AOF persistence)
redis:
  image: redis:7-alpine
  command: redis-server --appendonly yes --save 60 1