The error message is misleading. It happens if a client try to contact
the proxy entrypoint with the HTTP protocol without requesting an
upgrade to Websocket : only websocket requests can be tunneled to a
websockend endpoint, thus the proxy complains.
Your web application should have a subset of paths which use Websockets
and all other paths with plain HTTP(S). The correct config often boils
down to :
Proxy /ws ws://host:port/
Proxy /http://host:port/
And DON'T try to test by requesting the /ws URL with curl or your
browser, it will try plain HTTP(S) without asking for websocket upgrade
and Apache will complain with the message this bugreport mentions.
