workerd error: fetch failed socket hang up

workerd error: fetch failed socket hang up

TL;DR

The remote server closed the connection mid-fetch: it timed out, crashed, or rejected the request. Retry with backoff, check the remote's health, and set explicit timeouts (AbortSignal) so hangs fail fast instead of hanging the worker.

workerd error: fetch failed - socket hang up

Steps

1. Check the remote endpoint's health independently (curl from elsewhere). Expected: The remote's state is known.

2. Look for patterns: specific paths, payload sizes, or times of day. Expected: The trigger is identified.

3. Add retries with backoff and jitter for idempotent requests. Expected: Transient hangs are absorbed.

4. Set explicit timeouts via AbortSignal.timeout so hangs cannot stall the worker. Expected: Hangs fail fast.

5. If the remote is yours, check its connection handling (keepalive, timeouts, load). Expected: The server side is fixed.

When to use

• workerd fetch fails with socket hang up
• the remote is flaky
• fetches hang instead of failing

When not to use

• DNS fails (different error)
• the remote rejects with a status (that is an HTTP error, not a hang)
• all fetches fail (check the worker's network path)

Tool compatibility

• workerd
• Cloudflare Workers fetch

Variant phrasings

• "workerd socket hang up"
• "fetch failed socket hang up worker"
• "socket hang up cloudflare worker"

Why it happens

Socket hang up means the TCP connection died without an HTTP response: the server closed it, a proxy killed it, or a timeout fired. Workers feel it as a fetch rejection. The worker cannot fix the remote, but it can bound the damage with timeouts and retries.

Edge cases

• AbortSignal.timeout is the workerd-idiomatic timeout; use it
• retries need idempotency or they duplicate side effects
• keepalive mismatches between worker and origin cause exactly this

Provenance

Resolved from the public thread: https://vectle.com/posts/pstCfUuCXSrzaUiyre6-i4OA