[BUG] Proxmox web console fails to load via Zoraxy with 503 Service Unavailable error

[sannier3]

Describe the bug
The Proxmox web console does not display when accessed through Zoraxy. The interface loads, but the WebSocket connection required for the console fails with a 503 Service Unavailable error.

To Reproduce
Steps to reproduce the behavior:

1. Configure Zoraxy with the user interface for routing your Proxmox domain (e.g., https://<your-domain>).
2. Access the web interface at https://<your-domain>.
3. Log in and attempt to open a VM console.
4. The console fails to load, and the WebSocket connection shows a 503 Service Unavailable error.

Expected behavior
The Proxmox console should load successfully, allowing interaction with the virtual machine through the web interface.

Screenshots
Below is an example of the WebSocket request and the error response:

Request headers:

GET wss://proxmox.<hidden-domain>/api2/json/nodes/<node>/qemu/<vm-id>/vncwebsocket
Host: proxmox.<hidden-domain>
Connection: keep-alive, Upgrade
Upgrade: websocket
Sec-WebSocket-Version: 13
Sec-WebSocket-Key: [hidden] Origin: https://proxmox/.<hidden-domain>

Response headers:

HTTP/1.1 503 Service Unavailable
Content-Type: text/plain; charset=utf-8
X-Content-Type-Options: nosniff

Browser (if it is a bug appears on the UI section of the system):

• OS: [e.g. Windows 11]
• Browser [e.g. Chrome, Firefox]
• Version [e.g. 134.0.6958.2,134.0.1]

Host Environment (please complete the following information):

• Arch: [e.g. x86_64]
• Device: [e.g. Dell PowerEdge R720 | Proxmox VE 8.3.2]
• OS: [e.g. Debian 12]
• Version: [e.g. Latest v3.1.6]
• Docker Version (if you are running Zoraxy in docker): [e.g. 24.0.6]

Additional context
The Nginx configuration works as expected with the same Proxmox instance, indicating the issue is likely with Zoraxy's handling of WebSocket headers or backend communication.

The relevant Nginx configuration for reference:

proxy_set_header Connection $http_connection;
proxy_set_header Connection "upgrade";
proxy_set_header Origin http://$host;
proxy_set_header Upgrade $http_upgrade;
client_body_buffer_size 4m;
proxy_connect_timeout 7d;
proxy_send_timeout 7d;
proxy_read_timeout 7d;
proxy_cache off;
client_max_body_size 0;
proxy_max_temp_file_size 0;

The Zoraxy configuration includes:

• Custom headers for Upgrade, Connection, and Origin.
• EnableWebsocketCustomHeaders is set to true.

Further logs or details can be provided upon request.

[tobychui]

503 doesn't seems like a Zoraxy problem (Most issue we are seeing are 1006 and 501, which has been fixed earlier) . Have you read through the discussion over at #106 ? I guess that might bring you some insights on how to extract more information from the error you are currently seeing.