Patient #1

Getting 429 rate limit errors despite implementing exponential backoff

await fetch(url, {headers: {"Authorization": "Bearer " + token}})

The primary issue is likely that while exponential backoff is implemented, it's either not aggressive enough, not respecting the 'Retry-After' header provided by the server, or the rate limiting is being triggered by concurrent requests that are not being coordinated effectively. Exponential backoff alone doesn't guarantee success if the rate limit is very strict or if multiple requests are hitting the limit simultaneously from the same client without proper synchronization or global backoff state.

1. **Respect 'Retry-After' Header**: When a 429 is received, always check for a 'Retry-After' header in the response. If present, wait for at least the duration specified by this header before retrying. This is the most authoritative instruction from the server. 2. **Implement Jitter**: Add a small, random delay (jitter) to the exponential backoff. This prevents a 'thundering herd' problem where multiple clients (or multiple processes/threads within a single client) might all retry at the exact same time after an exponential backoff period. 3. **Increase Backoff Aggressiveness**: If 'Retry-After' is not present, ensure the exponential backoff increases significantly with each retry attempt, up to a reasonable maximum. 4. **Centralized Rate Limiting (Advanced)**: For highly concurrent applications, consider a centralized mechanism to track and enforce rate limits across all outgoing requests from your application, rather than just per-failed request. This might involve a token bucket or leaky bucket algorithm.