renku-vnc

1. Introduction

WORK IN PROGRESS.

Our objective is to run an X11 desktop and applications inside a jupyterlab based docker container, and display them in an HTML canvas present through our jupyterlab interface or full screen. Because the container is deployed and managed by renkulab, whatever method we use must piggy back on the existing jupyter connection.

A VNC-based approach with a javascript RFB to HTML5 renderer seems to be the easiest solution.

We try and compare the methods below.

In all configurations we use novnc in order to render the RFB events into HTML on the browser side. All are served behind a Jupyter server proxy inside a Docker container, except for the nginx approach which is used only for debugging purpose.

2. Configurations

2.1 Jupyter server proxy - novnc+websockify - x11vnc - xvbf

• Advantages

  • It just works
  • Xvbf built on native OS distributor’s X.org/X11 implementation, for better compatibility

• Disadvantages

  • overhead of x11vnc on top of xvbuf (to be confirmed in this exercise)
  • More proxies than required? websockify may not be necessary if libvncserver, on which x11vnc is built, supports websockets

• Implementation details

• Try it on renkulab.io

2.2 Jupyter server proxy - novnc - x11vnc - xvbf

• Advantages

  • It is supposed to work
  • Xvbf built on native OS distributor’s X.org/X11 implementation, for better compatibility
  • Take advantage of libvncserver’s support for websockets and get away without the need for websockify

• Disadvantages

  • overhead of x11vnc on top of xvbf (to be confirmed in this exercise)

• Caveats

  • Libvncserver theoretically supports websocket, but see novnc’s issue 1310), and all related issues.

2.3 Jupyter server proxy - novnc+websockify - TigerVNC (Xvnc)

• Advantages

  • TigerVNC (Xvnc) built on native OS distributor’s X.org/X11 implementation, for better compatibility
  • Remove overhead of separate x virtual frame buffer xvfb and vnc server, TigerVNC combines both in one

• Disavantages

  • No support for websockets? can’t get away without overhead of intermediate websockify

• Implementation details

• Try it on renkulab.io

2.4 In-house solution

After investigating all the above configurations, we may find out that we prefer XRDP after all, or that we are better off forking our own VNC server implementation or novnc-like solution, optimised for our use case that is cusomized for our needs.

3. Development

3.1 Nginx

We include this nginx configuration for testing and debugging the above configurations. It can be used to test the Docker container with the VNC stack outside the renkulab or jupyterlab context, and to serve the novnc js code and proxify the websocket connection through a same port.

• Install nginx as root or sudoer

  release=$(grep -Po '(?<=VERSION_CODENAME=).*' /etc/os-release)
  echo "deb https://nginx.org/packages/ubuntu/ ${release:-bionic} nginx
  deb-src https://nginx.org/packages/ubuntu/ ${release:-bionic} nginx
  " > /etc/apt/sources.list.d/nginx.list
  sudo apt-get update
  sudo apt-get install nginx

If you get the GPG error: https://nginx.org/packages/ubuntu xenial Release: The following signatures couldn’t be verified because the public key is not available: NO PUBKEY $key:

Take note of $key, and replacing $key by its proper value, run

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys $key
sudo apt-get update
sudo apt-get install nginx

• Create a simple novnc virtual host in /var/www/noVNC/ with the novnc resources as root or sudoer

  cd /var/www
  git clone https://github.com/novnc/noVNC.git
  cd noVNC
  rm -rf .git

• Configure nginx http context for websocket, as root or sudoer, e.g. create an ws.conf file

  "${EDITOR:-vi}" /etc/nginx/conf.d/ws.conf

And copy the text below

##
# Websockets
##
map $http_upgrade $connection_upgrade {
    default upgrade;
    ''      close;
}

• Create a virtual host

  "${EDITOR:-vi}" /etc/nginx/sites-enabled/vnc

And copy the text below

server {
    listen 8888;
    listen [::]:8888;
    error_log /tmp/nginx.tmp warn;
    server_name jupyter.renkulab.io;
    root /var/www/noVNC;
    location / {
        index vnc_lite.html;
        try_files $uri $uri/ =404;
    }
    location /ws/ {
        proxy_pass http://localhost:5901;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
        proxy_set_header Host $host;
    }
}

• Build the image, and start your container with docker run --rm -it -p 8888:8888 image-name /bin/bash

• Run service nginx restart inside the container to start the ngnix service

You can now access the vnc page on localhost:8888/vnc.html?path=/ws/. There must be a VNC service (RFB protocol) with websocket support listening on 5901. See the methods presented above for the different types of VNC sever (without the jupyter server proxy).

• Notes:

  • In the example, port 8888 is used to connect from the host computer to nginx listening on port 8888 inside the docker container
  • Inside the container, nginx maps / locations to files under /var/www/noVNC, and streams the /ws/ location to localhost:5901
  • A VNC service supporting the websocket RFB protocol must listen on port 5901 inside the container.

• Notes:

  • This is WIP - novnc’s RFB client can connect to x11vnc service which dumps protocol handshake logs that appear normal. However connection hangs and times out - it could be related to the libvncserver bugs mentioned above (there are several references to it). Updating libvncserver as recommended as a quick fix did not seem to help. This is under investigation while I am reviewing the logs.

3.2. Substituting Xdummy for Xvfb

It is possible to configure the Dockerfile to use the Xdummy as the headless X server instead of Xvfb. This is mostly applicable to the x11vnc option, since TigerVNC/Xvnc include the X server.

• Install xorg’s dummy server if it is not provided with x11vnc

apt-get install xserver-xorg-video-dummy

Create a /usr/bin/Xdummy executable (chmod 755) containing the following script

#!/usr/bin/env bash
Xorg -noreset +extension GLX +extension RANDR +extension RENDER -logfile /tmp/20.log -config /etc/xorg.conf :20

You must provide the /etc/xorg.conf configuration file. See xpra’s xorg.conf as an example.

• Modify the -display parameter of your x11vnc command so that it uses Xdummy (and falls back on Xvfb)

  -display WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb \

• Using this configuration the resizing should automatically be taken care of remotely by the server. If needed at runtime, you can manually adjust the default geometry with xrandr

xrandr --output default --mode 1280x1024

3.3. Weston in Wayland?

We do not consider Wayland for our Docker container yet.

This is because wayland needs to run an X server behind the scene in order to process client inputs that it can’t understand, resulting in a higher memory and CPU usage.

3.4. TODO

• We did not try to optimize of the X server and VNC server parameter configuration for better performance or stability. Our first focus is to achieve a usable configuration.
• Clipboard cut/paste is currently not working (tested on macos).
• Consider using supervisord and start-stop-daemon