Cache-aside pattern: how to implement read-through caching in Node.js

Cache-aside (lazy loading)

Cache-aside is the most common caching pattern. Your application code manages the cache manually: check Redis first, fetch from the database on a miss, then populate Redis.

Implementation in Node.js

const redis = require('redis');
const client = redis.createClient();

async function getUser(userId) {
  const cacheKey = `user:${userId}`;

  // 1. Check cache
  const cached = await client.get(cacheKey);
  if (cached) return JSON.parse(cached); // cache hit

  // 2. Cache miss — fetch from DB
  const user = await db.query('SELECT * FROM users WHERE id=$1', [userId]);

  // 3. Populate cache with TTL
  await client.setEx(cacheKey, 300, JSON.stringify(user));
  return user;
}

Tradeoffs

Cache-aside is simple and only caches what is actually requested. The downside is the first request after a cache miss is slow. Under high traffic, many concurrent misses for the same key can hammer the database simultaneously — this is called a cache stampede. Mitigate it with a mutex lock (covered in Module 5) or probabilistic early expiration.

Always set a TTL. A cache without TTLs will eventually serve stale data indefinitely.