How to pass ECONNREFUSED through the proxy

[martinschayna]

I have a proxy that rewrites requests to couple of servers on the same machine running on different ports. It should be transparent as possible, so when some of target servers aren't running, I want to pass ECONNREFUSED error to the client.

That should be possible inside onError handler, default handler looks like that:

function onError(err, req, res, target) {
  res.writeHead(504, { 'Content-Type': 'text/plain' });
  res.end('Something went wrong. And we are reporting a custom error message.');
}

but obviously, that's not the same, client gives 504 instead of error. What could I put into onError handler to simulate original error in client? Thanks.

[chimurai]

What you're trying to do, contradicts with the error code ECONNREFUSED.

You'll only make debugging more difficult by actually returning a response with the ECONNREFUSED error...

Returning a 502 might be a better practice and log the real ECONNREFUSED for tracing and debugging.

The HyperText Transfer Protocol (HTTP) 502 Bad Gateway server error response code indicates that the server, while acting as a gateway or proxy, received an invalid response from the upstream server.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/502