OK, finally got it to work.. and yes, if web-sockets is not used, printing will not work!
here are fragment of my Apache virtual site:
ProxyPass /websocket-tunnel ws://YOURIP:PORT/guacamole/websocket-tunnel
ProxyPassReverse /websocket-tunnel ws://YOURIP:PORT/guacamole/websocket-tunnel
ProxyPass / http://YOURIP:PORT/guacamole/ flushpackets=on
ProxyPassReverse / http://YOURIP:PORT/guacamole/
keep in mind about order - first you need to specify web-socket section, and then the main page section - according to guac docs, they wrote you need to do it vice-versa... BUT, their Docs don't contain any examples with sub-domain at all..
So, fingers crossed for me!
@Taddeusz, my next question is about file exchange between host and client. what is a recommended way? cos Clients are connected to server from various locations, so i'm not sure, how to map client local drive to upload/download files to server..