This was happening for me in my Apache/2.4.18 (Ubuntu) setup. In my case, the error I was seeing was:
... AH01144: No protocol handler was valid for the URL /~socket.io/. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
The configuration related to this was:
ProxyPass /~socket.io/ ws://127.0.0.1:8090/~socket.io/
ProxyPassReverse /~socket.io/ ws://127.0.0.1:8090/~socket.io/
"No protocol handler was valid for the URL /~socket.io/
" meant that Apache could not handle the request being sent to "ws://127.0.0.1:8090/~socket.io/
"
I had proxy_http
loaded, but also needed proxy_wstunnel
. Once that was enabled all was good.