API Throttling Mechanisms

🚦 API Throttling Mechanisms

APIs are powerful gateways to your app’s core functionality — but with great power comes great responsibility. If you leave your API unguarded, it can be overwhelmed by misuse, spam, or even DDoS attacks.

That’s where API Throttling comes in — your first line of defense for maintaining server health and fair usage 🌐.

🔍 What is API Throttling?

API throttling is the process of limiting how many requests a client can make to your API in a given timeframe.

Think of it as a traffic light 🚦 — it slows things down to prevent jams or crashes.

For example, you might allow:

• ⏱️ 100 requests per user per minute
• 💥 Block the IP for a cooldown period if exceeded
• 📊 Log excessive usage for analysis

🧠 Why Throttle API Usage?

• 🛡️ Prevent abuse and brute-force attacks
• 📉 Avoid server overload and downtime
• ⚖️ Ensure fair usage among users
• 💰 Optimize resource consumption (especially in cloud environments)

⚙️ Implementing Throttling in Bun

Bun doesn’t ship with built-in throttling (yet), but it’s fast enough that you can implement it yourself or plug in a middleware.

Let's build a simple in-memory rate limiter based on IP address.

const rateLimitMap = new Map();

const RATE_LIMIT = 100; // max 100 requests
const TIME_WINDOW = 60 * 1000; // in 60 seconds

Bun.serve({
  port: 3000,
  fetch(req) {
    const ip = req.headers.get("x-forwarded-for") || "unknown";
    const now = Date.now();

    const data = rateLimitMap.get(ip) || { count: 0, start: now };

    if (now - data.start < TIME_WINDOW) {
      data.count++;
      if (data.count > RATE_LIMIT) {
        return new Response("🚫 Rate limit exceeded", { status: 429 });
      }
    } else {
      data.count = 1;
      data.start = now;
    }

    rateLimitMap.set(ip, data);
    return new Response("✅ Request accepted");
  }
});

This simple mechanism prevents abuse per IP and resets after each minute ⏳.

🛠️ Use Case: Throttling Based on API Keys

You can also throttle users based on their API key or user ID.

Just change the key in the map:

const apiKey = new URL(req.url).searchParams.get("key") || "guest";

Then use apiKey instead of ip in your limiter. That way, even shared IPs (e.g., proxies) don’t affect others 🌐.

🚀 Using Redis for Distributed Rate Limiting

Need to scale? If you're running multiple Bun instances, in-memory throttling won't cut it.

Use Redis to share limits across servers:

// Pseudo-code — requires a Redis client like ioredis
await redis.incr(apiKey);
await redis.expire(apiKey, 60);

This lets you throttle globally across multiple nodes without collisions ☁️.

📦 Third-Party Throttling Libraries

If you don’t want to reinvent the wheel, you can integrate established libraries with Bun using ESM-compatible modules:

• ⛽ rate-limiter-flexible – Redis or Memory backend
• 🔌 Custom WebSocket throttling middleware
• 🔒 JWT-based usage limits per plan/tier

🔐 Throttling + Authentication = 💪

Combine throttling with auth for tiered plans:

• 🆓 Free plan – 60 requests/min
• 💼 Pro plan – 500 requests/min
• 🏢 Enterprise – unlimited (with monitoring!)

📈 Monitoring Throttled Requests

You should always log or analyze throttle events to understand usage patterns.

This helps you:

• 📊 Detect high-traffic users
• 🚨 Spot abuse or bots
• 🔧 Tune your rate limit settings

🧪 Testing Your Throttling Logic

Use autocannon or k6 to simulate high traffic.

Ensure:

• 🟢 Normal usage passes
• 🔴 Overuse gets blocked with 429
• 📆 Limits reset over time

🏁 Conclusion

API Throttling mechanisms are critical to protect your server, your users, and your business model. Whether you're building with Bun or any other stack, start with simple in-memory throttling and scale out with Redis or third-party tools when needed.