I briefly attempted to reproduce on 4.11.0 but so far have not seen the slowness with proxy-domain nor have I seen the res.writeHead error.

I used localhost as my proxy domain (so <port>.localhost:8080). For my web service I ran python -m http.server 8000. Might have to try fastapi and a real domain.

Code-wise I am not sure how this would happen; the proxy domain flag is checked against the host on each request but crazy for that to take nearly two minutes! Does this reliably reproduce for you when you add/remove the proxy-domain flag?

@code-asher Thanks for looking into it. I tried this again today and was not able to reproduce the slowness. I've been hosting this on a GCP compute engine instance and wonder if there were intermittent issues on that side.
However I am still getting the res.writeHead error in the logs, this only shows up with proxy-domain flag. I am not really familiar with nginx and have just followed guides to get that set up, so I wonder if I have mis-configured something that is triggering this.

This is my nginx file:

server {
    server_name code.example.com *.code.example.com;

    location / {
      proxy_pass http://localhost:8080/;
      proxy_set_header Host $host;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection upgrade;
      proxy_set_header Accept-Encoding gzip;
    }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/code.example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/code.example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot



}
server {
    if ($host = *.code.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = code.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    listen 80;
    listen [::]:80;
    server_name code.example.com *.code.example.com;
    return 404; # managed by Certbot
}

Let me know if there's anything I can do to help test/figure out where the error is coming from.

That config looks good to me. The res.writeHead in question runs when the proxy fails to hit the target and I think maybe writeHead is undefined when the request is a web socket.

Aha yup I am able to reproduce with new WebSocket("wss://localhost:8080/proxy/8000") where I have nothing running on 8000.

We will need to handle the code differently, something like this should work.

res.end(`HTTP/1.1 ${statusCode} ${err.message}\r\n\r\n`)

In the meantime, is your app opening web sockets to the right spot?