Hedgedoc has some difficulties to communicate with the server with websockets.
The protocol falls back to web polling causing some weird behaviors during parallel editions (lost content, duplicate characters, ...)
websocket.js:124 WebSocket connection to 'wss://hedgedoc.softwareheritage.org/socket.io/?noteId=features&EIO=3&transport=websocket&sid=<redacted> failed: Error during WebSocket handshake: Unexpected response code: 404
The cause seems to be a wrong backend routing in varnish for the upgrade requests only:
* << BeReq >> 73173170 - Begin bereq 73173169 pipe - BereqMethod GET - BereqURL /socket.io/?noteId=features&EIO=3&transport=websocket&sid=<redacted> - BereqProtocol HTTP/1.1 - BereqHeader Host: hedgedoc.softwareheritage.org - BereqHeader Connection: Upgrade - BereqHeader Pragma: no-cache - BereqHeader Cache-Control: no-cache - BereqHeader User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.75 Safari/537.36 - BereqHeader Origin: https://hedgedoc.softwareheritage.org - BereqHeader Sec-WebSocket-Version: 13 - BereqHeader Accept-Encoding: gzip, deflate, br - BereqHeader Accept-Language: en-US,en;q=0.9,fr;q=0.8 - BereqHeader Cookie: connect.sid=s%<redacted>; indent_type=space; space_units=4; keymap=sublime; loginstate=false - BereqHeader Sec-WebSocket-Key: <redacted>wg== - BereqHeader Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits - BereqHeader X-Forwarded-For: xx.xx.xx.xx - BereqHeader X-Varnish: 73173169 - BereqUnset Connection: Upgrade - BereqHeader Connection: close - VCL_call PIPE - BereqHeader upgrade: websocket - BereqUnset Connection: close - BereqHeader connection: Upgrade - BereqUnset upgrade: websocket - BereqHeader upgrade: websocket - BereqUnset connection: Upgrade - BereqHeader connection: Upgrade - VCL_return pipe - BackendOpen 95 grafana 192.168.xx.xx 3000 192.168.xx.xx 59022 connect <---------------- wrong backend - Timestamp Bereq: 1650561229.210203 0.000000 0.000000 - BackendClose 95 grafana close - BereqAcct 0 0 0 0 0 0 - End