How to design a rate limiter for an API

Short answer

Implement rate limiting at the gateway or application layer using algorithms like token bucket or sliding window counter. Store counters in a fast key-value store like Redis. For distributed rate limiting, see how caching improves system performance. For infrastructure choices, see how to choose a cloud provider.

Steps

1. Choose an algorithm: token bucket, leaky bucket, or sliding window
2. Store counters in a centralized cache with TTL
3. Enforce limits before processing expensive business logic
4. Return appropriate HTTP status codes: 429 Too Many Requests
5. Monitor and alert on rate limit hits

Tips

• Use different limits per user tier or API endpoint
• Implement exponential backoff guidance in response headers
• For cost optimization, review how to design for cloud cost optimization