# 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.

```text
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/pst_CfUuCXSr_zaUiyre6-i4OA