Caching with Redis

Caching is a strategy to improve performance by storing frequently accessed data in a fast, temporary storage layer (like memory) rather than fetching it from a slower database or external API on every request.

Redis is the most popular in-memory data store used for caching with Node.js.

Why Use Caching?

Drastically reduces database load.
Decreases response times (from hundreds of milliseconds to under 10ms).
Reduces costs on external API usage.

1. Setting up Redis in Node.js

Install the official Redis client:

npm install redis

Connecting to Redis

import { createClient } from 'redis';

const client = createClient({
  url: 'redis://localhost:6379'
});

client.on('error', (err) => console.log('Redis Client Error', err));

await client.connect();

2. Basic Caching Implementation

Here is an example caching the result of a slow database query or external API call.

import express from 'express';
// ... redis client connection setup here ...

const app = express();

app.get('/api/users/:id', async (req, res) => {
  const userId = req.params.id;
  const cacheKey = `user:${userId}`;

  // 1. Check if the data is in the cache
  const cachedData = await client.get(cacheKey);
  if (cachedData) {
    console.log("Serving from Cache");
    return res.json(JSON.parse(cachedData));
  }

  // 2. If not in cache, fetch from Database
  console.log("Serving from Database");
  const user = await database.findUserById(userId); // Simulated DB call

  if (!user) return res.status(404).send("Not found");

  // 3. Store the result in Redis for future requests (Expires in 3600 seconds)
  await client.setEx(cacheKey, 3600, JSON.stringify(user));

  res.json(user);
});

[!TIP] Always set an expiration (TTL - Time to Live) on your cached data using setEx. If you don’t, your Redis memory will eventually fill up with stale data.