Understanding 429 (Too Many Requests) & Throttling Pattern

What is 429?

HTTP status code 429 "Too Many Requests" indicates that a user has sent too many requests in a given amount of time. This is also known as "rate limiting" or "throttling."

Best Practices for Handling 429

1. Server-side:

   • Include Retry-After header in the response

   • Use sliding window or token bucket algorithms for accurate rate limiting

   • Maintain separate limits for different API endpoints

2. Client-side:

   async function apiCall() {
     try {
       const response = await fetch('/api/resource');
       if (response.status === 429) {
         const retryAfter = response.headers.get('Retry-After');
         await delay(retryAfter * 1000);
         return apiCall(); // Retry request
       }
       return response.json();
     } catch (error) {
       console.error('Request failed:', error);
     }
   }

Common Throttling Strategies

1. Fixed Window: Simplest but can allow bursts at window boundaries

2. Sliding Window: More accurate, prevents boundary bursts

3. Token Bucket: Flexible, allows for burst handling while maintaining average rate

4. Leaky Bucket: Smooths out request processing, good for queue-based systems

By implementing proper throttling and 429 handling, you can protect your services while providing a better experience for all users.