Redis & Caching Strategies

1// Redis & Caching — Production Patterns
2
3const Redis = require("ioredis");
4
5// 1. Redis connection with retry
6const redis = new Redis({
7  host: process.env.REDIS_HOST || "localhost",
8  port: parseInt(process.env.REDIS_PORT || "6379"),
9  password: process.env.REDIS_PASSWORD,
10  maxRetriesPerRequest: 3,
11  retryStrategy(times) {
12    const delay = Math.min(times * 50, 2000);
13    return delay;
14  },
15  lazyConnect: true,
16});
17
18redis.on("connect", () => console.log("Redis connected"));
19redis.on("error", (err) => console.error("Redis error:", err.message));
20
21// 2. Cache-Aside pattern (most common)
22async function getUserWithCache(userId) {
23  const cacheKey = `user:${userId}`;
24
25  // Check cache
26  const cached = await redis.get(cacheKey);
27  if (cached) {
28    console.log("Cache HIT");
29    return JSON.parse(cached);
30  }
31
32  // Cache miss — fetch from database
33  console.log("Cache MISS");
34  // const user = await db.user.findById(userId);
35  const user = { id: userId, name: "Alice", email: "alice@example.com" }; // Mock
36
37  // Store in cache with TTL (5 minutes)
38  await redis.set(cacheKey, JSON.stringify(user), "EX", 300);
39
40  return user;
41}
42
43// 3. Cache middleware for Express
44function cacheMiddleware(ttlSeconds = 300) {
45  return async (req, res, next) => {
46    // Only cache GET requests
47    if (req.method !== "GET") return next();
48
49    const cacheKey = `cache:${req.originalUrl}`;
50
51    try {
52      const cached = await redis.get(cacheKey);
53      if (cached) {
54        return res.json(JSON.parse(cached));
55      }
56    } catch (err) {
57      console.error("Cache read error:", err.message);
58    }
59
60    // Store original res.json to intercept
61    const originalJson = res.json.bind(res);
62    res.json = (data) => {
63      // Cache the response
64      redis.set(cacheKey, JSON.stringify(data), "EX", ttlSeconds).catch(console.error);
65      return originalJson(data);
66    };
67
68    next();
69  };
70}
71
72// 4. Cache invalidation on write
73async function updateUser(userId, data) {
74  // Update database
75  // const user = await db.user.update(userId, data);
76  const user = { id: userId, ...data };
77
78  // Invalidate cache
79  await redis.del(`user:${userId}`);
80
81  // Also invalidate list caches
82  const keys = await redis.keys("cache:/api/users*");
83  if (keys.length > 0) await redis.del(...keys);
84
85  return user;
86}
87
88// 5. Rate limiting with Redis
89async function checkRateLimit(clientId, maxRequests = 100, windowSeconds = 60) {
90  const key = `ratelimit:${clientId}`;
91  const current = await redis.incr(key);
92
93  if (current === 1) {
94    await redis.expire(key, windowSeconds);
95  }
96
97  return {
98    allowed: current <= maxRequests,
99    remaining: Math.max(0, maxRequests - current),
100    resetIn: await redis.ttl(key),
101  };
102}
103
104// 6. Session storage with Redis
105async function sessionExample() {
106  const sessionId = "sess_abc123";
107  const sessionData = {
108    userId: 1,
109    role: "admin",
110    loginTime: Date.now(),
111  };
112
113  // Store session (24 hour TTL)
114  await redis.set(`session:${sessionId}`, JSON.stringify(sessionData), "EX", 86400);
115
116  // Retrieve session
117  const session = JSON.parse(await redis.get(`session:${sessionId}`));
118
119  // Extend session on activity
120  await redis.expire(`session:${sessionId}`, 86400);
121
122  // Destroy session (logout)
123  await redis.del(`session:${sessionId}`);
124}
125
126// 7. Pub/Sub for real-time events
127async function pubSubExample() {
128  const subscriber = redis.duplicate();
129
130  subscriber.subscribe("notifications", (err) => {
131    if (err) console.error("Subscribe error:", err);
132  });
133
134  subscriber.on("message", (channel, message) => {
135    console.log(`[${channel}] ${message}`);
136  });
137
138  // Publish from another part of the app
139  await redis.publish("notifications", JSON.stringify({
140    type: "order_placed",
141    orderId: 123,
142  }));
143}
144
145module.exports = { redis, cacheMiddleware, checkRateLimit };