WebSocket 502 error

Infos:

  • Used Zammad version: 3.6.x
  • Used Zammad installation source: CentOS 7 package
  • Operating system: CentOS 7
  • Browser + version: Google Chrome (newest)
  • Firewall: Sophos XG

Actual behavior:

[error] 18835#0: *558 upstream prematurely closed connection while reading response header from upstream, client: xxx.xxx.xxx.xxx, server: support.xxx.ch, request: “GET /ws HTTP/1.1”, upstream: “http://127.0.0.1:6042/ws”, host: “support.xxx.ch”

Steps to reproduce the behavior:

Everything works properly in the internal network.Only as soon as the chat is to be accessed externally via the Sophos XG, I get the following message in the browser:
WebSocket connection to ‘wss://support.xxx.ch/ws’ failed: Error during WebSocket handshake: Unexpected response code: 502
e.connect @ chat.min.js:1
(anonymous) @ chat.min.js:1
e @ chat.min.js:1
(anonymous) @ (index):525
j @ jquery.js?ac63be:2
fireWith @ jquery.js?ac63be:2
ready @ jquery.js?ac63be:2
K @ jquery.js?ac63be:2

Sophos firewalls tend to break websocket connections if they’re playing proxy.
This is a sophos related issue - please ensure it allows websockets between your client and Zammad in order to reduce load and function proper.

This is a very specific problem which may not find a resolution on this board as it’s application specific. Sorry