Please read and configure accordingly:
http://docs.haproxy.org/2.8/configuration.html#proto%20(Bind%20options)
http://docs.haproxy.org/2.8/configuration.html#proto%20(Server%20and%20default-server%20options)
http://docs.haproxy.org/2.8/configuration.html#ws
http://docs.haproxy.org/2.8/configuration.html#3.1-h2-workaround-bogus-websocket-clients