Server-Side API Response Caching with Node.js and Redis

const express = require('express');
const axios = require('axios'); // For making external API calls
const redis = require('redis');

const app = express();
const PORT = process.env.PORT || 3000;
const REDIS_PORT = process.env.REDIS_PORT || 6379;
const EXTERNAL_API_URL = 'https://jsonplaceholder.typicode.com/posts'; // Example API

// Create Redis client
const redisClient = redis.createClient({
  port: REDIS_PORT,
  // host: 'your_redis_host' // Uncomment and set if Redis is not on localhost
});

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

// Connect to Redis (async operation)
(async () => {
  await redisClient.connect();
})();

// Middleware to cache API responses
const cacheMiddleware = async (req, res, next) => {
  const cacheKey = req.originalUrl; // Use the request URL as the cache key
  
  try {
    const cachedData = await redisClient.get(cacheKey);
    if (cachedData) {
      console.log(`Cache hit for ${cacheKey}`);
      return res.send(JSON.parse(cachedData));
    }
    console.log(`Cache miss for ${cacheKey}`);
    // If not in cache, proceed to the route handler to fetch data
    next();
  } catch (err) {
    console.error('Redis cache error:', err);
    next(); // Continue without caching if Redis has issues
  }
};

// Route to fetch data from the external API with caching
app.get('/api/posts', cacheMiddleware, async (req, res) => {
  try {
    const { data } = await axios.get(EXTERNAL_API_URL);
    
    // Store data in Redis with an expiration time (e.g., 60 seconds)
    await redisClient.setEx(req.originalUrl, 60, JSON.stringify(data));
    
    res.send(data);
  } catch (error) {
    console.error('Error fetching from external API:', error.message);
    res.status(500).send('Failed to fetch data from external API');
  }
});

// Basic route for non-cached content
app.get('/', (req, res) => {
  res.send('Welcome to the API cache example!');
});

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
  console.log(`Open http://localhost:${PORT}/api/posts to test caching.`);
});