Viewing Dockerised Desktops via an X11 Bridge, novnc and RDP, Sort of…

So… the story so far…

As regular readers of this blog will know, I happen to be of the opinion that we should package more of OUr software using Docker containers, for a couple of reasons (at least):

  • we control the software environment, including all required dependencies, and avoiding any conflicts with preinstalled software;
  • the same image can be used to launch containers locally or remotely.

I also happen to believe that we should deliver all UIs through a browser. Taken together with the containerised services, this means that students just need a browser to run course related software. Which could be on their phone, for all I care.

I keep umming and ahhing about electron apps. If the apps that are electron wrapped are also packaged so that they can also be run as a service and accessed via a browser too, that’s fine, I guess…

There are some cases in which this won’t work. For example, not all applications we may want to distribute come with an HTML UI, but instead may be native applications (which is an issue becuase we are supposed to be platform independent), or cross platform applications that use native widgets (for example, Java apps, or electron apps).

One way round this is to run a desktop application in container and then expose its UI using X11, (aka the X Window System), although this looks like it may be on the way out in favour of other windowing alternatives, such as Wayland… See also Chrome OS Is Working To Remove The Last Of Its X11 Dependencies. (I am so out of my depth here!)

Although X11 does provide a way of rendering windows created on a remote (or containerised guest) system using native windows on your own desktop, a downside is that it requires X11 support on your own machine; and I haven’t found a cross-platform one that looks to be a popular de facto standard.

Another approach is to use VNC, in which the remote (or guest) system sends a compressed rendered version of the desktop back to your machine, which then renders it. (See X11 on Raspberry Pi – remote login from your laptop for a discussion of some of the similarities and differences between X11 and VNC.)

Note to self – one of the issues I’ve had with VNC is the low screen resolution of the rendered desktop… but is that just because I used a default low resolution in the remote VNC server? Another issue I’ve had in the past with novnc, a VNC client that renders desktops using HTML via a browser window, relates to video and audio support… Video is okay, but VNC doesn’t do audio?

Earlier today, I came across x11docker, that claims to run GUI applications and desktops in docker (though on Windows and Linux desktops only. The idea is that you “just type x11docker IMAGENAME [COMMAND]” to launch a container and an X11 connection is made that allows the application to be rendered in a native X11 window. You can find a recipe for doing something similar on a Mac here: Running GUI’s with Docker on Mac OS X.

But that all seems a little fiddly, not least because of a dependency on an X11 client which might need to be separately installed. However, it seems that we can use another Docker container — JAremko/docker-x11-bridge — running xpra (“an open-source multi-platform persistent remote display server and client for forwarding applications and desktop screens”) as bridge that can connect to an X11 serving docker container and render the desktop in a browser.

For example, Jess Frazelle’s collection of Dockerfiles containerise all manner of desktop applications (though I couldn’t get them all to work over X11; maybe I wasn’t starting the containers correctly?). I can get them running, in my browser, by starting the bridge:

docker run -d \
 --name x11-bridge \
 -e MODE="tcp" \
 -e XPRA_HTML="yes" \
 -e DISPLAY=:14 \
 -p 10000:10000 \

and then firing up a couple of applications:

docker run -d --rm  \
  --name firefox \
  --volumes-from x11-bridge \
  -e DISPLAY=:14 \

docker run -d --rm  \
  --name gimp \
  --volumes-from x11-bridge \
  -e DISPLAY=:14 \

#docker kill gimp firefox
#docker rm gimp firefox
#docker rmi jess/gimp jess/firefox

Another approach is to use VNC within a container, an approach I’ve used with this DIT4C Inspired RobotLab Container/ (The DIT4C container is quite old now; perhaps there’s something more recent I should use? In particular, audio support was lacking.)

It’s been a while since I had a look around for good examples of novnc containers, but this Collection of Docker images with headless VNC environments could be a useful start:

Desktop environment Xfce4 or IceWM
VNC-Server (default VNC port 5901)
noVNC – HTML5 VNC client (default http port 6901)

The containers also allow screen resolution and colour depth to be set via environment variables. The demo seems to work (without audio) using novnc in a browser, and I can connect using TigerVNC to the VNC port, though again, without audio support.

Audio is a pain. On a Linux machine, you can mount an audio device when you start a novnc container (eg fcwu/docker-ubuntu-vnc-desktop) but I’m not sure if that works on a Mac? Or how it’d work on Windows?) That said, a few years ago I did find a recipe for getting audio out of a remote container that did seem to work — More Docker Doodlings – Accessing GUI Apps Via a Browser from a Container Using Guacamole — although it seems to be broken now (did the container format change in that period I wonder?). Is there a more recent (and robust) variant of this out there somewhere, I wonder?

Hmm… here’s another approach: using a remote desktop client. Microsoft produce RDP (Remote Desktop Protocol) clients for different platforms so that might provide a useful starting point.

This repo — danielguerra69/firefox-rdp — builds on danielguerra69/dockergui (fork of this) and shows how to create a container running Firefox that can be accessed via RDP. If I run it:

docker run --rm -d --shm-size 1g -p 3389:3389 --name firefox danielguerra/firefox-rdp

I can create a connection using the Microsoft remote desktop client at the address localhost:3389, login with my Mac credentials, and then use the application. Testing on Youtube shows that video and audio work too. So that’s promising…

(Docker housekeeping: docker kill firefox; docker rm firefox; docker rmi danielguerra/firefox-rdp.)

Hmmm… so maybe now we’re getting somewhere more recent. Eg danielguerra69/ubuntu-xrdp although this doesn’t render the desktop properly for me, and danielguerra69/alpine-xfce4-xrdp doesn’t play out the audio? Ah, well… I’ve wasted enough time on this for today…

Browser Based Virtualised Environments for Cybersecurity Education – Labtainers and noVNC

Whilst my virtualisation ramblings may seem to be taking a scattergun approach, I’m actually trying to explore the space in a way that generalises meaningfully in the context of the open and distance education.

The motivating ideas essentially boil down to these two questions / constraints:

  • can we package a software application once that we can then run it cross-platform, anywhere, both locally and remotely?
  • can we package the same software application so that it is available via a universal client? I tend to favour the browser as a universal client, but until I can figure out how to do audio from remote desktops via a browser, I also appreciate there may be a need for something like an RDP client too.

I’m also motivated by “open” on the one hand – can we share the means of production, as well as the result — and factory working: will the approach used to deliver one application scale to other applications in different subject areas, or the same application, over time, as it goes through various versions.

My main focus has been on environments for running our TM351 applications (Jupyter notebooks, various databases, OpenRefine) as well as keeping legacy applications running (RobotLab, Genie, Daisyworld) as well as exploring other virtualised desktops (eg for the VREP simulator) but there is also quite a lot of discussion internally around used virtualised environments to support our cybersecurity courses.

I suspect this is both a mature and an evolving space:

  • mature, in that folk have been using virtual machines to support this sort of course for some time; for example, this Offline Capture The Flag-Style Virtual Machine for Cybersecurity Education from University of Birmingham that dates back to 2015, or this SEED Labs — Hands-on Labs for Security Education from Syracuse University that looks like it dates back to 2002. There is also the well-known Kali Linux distribution that is widely used for digital forensics, penetration testing, ethical hacking training, and so on. (The OU also has a long standing Masters level course that has been using a VM for years…)
  • emerging, in that the technology for packaging (eg Docker) and running (eg the growth in cloud services) is evolving quickly, as are the increasing opportunities for creating things like structured notebook scripts around cybersecurity activities).

Recently, I also came across Labtainers, a set of virtual machines produced by the US Naval Postgraduate School’s Center for Cybersecurity and Cyber Operations billed as “fully packaged Linux-based computer science lab exercises with an initial emphasis on cybersecurity. Labtainers include more than 40 cyber lab exercises and tools to build your own.”

Individual activities are packaged in individual Docker containers, and a complete distribution is available bundled into a VirtualBox virtual machine (there’s also a Labtainer design guide). There’s also a paper here: Individualizing Cybersecurity Lab Exercises with Labtainers, Michael F. Thompson & Cynthia E. Irvine, IEEE Security & Privacy, Vol 16(2), March/April 2018, pp. 91-95, DOI: 10.1109/MSP.2018.1870862.

I actually spotted Labtainers from a demo by Olivier Berger / @olberger that was in part demonstrating a noVNC bridge container he’s been working on. I first posted about an X11 / XPRA bridge container I’d come across here; that post describes the JAremko/docker-x11-bridge container which I can run to provide an noVNC desktop through my browser; we can then run application separate application containers and mount the bridge container as a device, exposing the container application on the noVNC desktop. Olivier’s patched noVNC desktop container (fcwu/docker-ubuntu-vnc-desktop offers access to “an Ubuntu LXDE and LXQT desktop environment” so that it can be used in a similar way.

You can see it in action with the labtainers here:

A supporting blog post can be found here: Labtainers in a Web desktop through noVNC X11 proxy, full docker containers; there’s also an associated repo.

From the looks of it, Olivier has been on a similar journey to myself. Another post, this time from last year, describes a Demo of displaying labtainers labs in a Web browser through Guacamole (repo). Guacamole is an Apache project that provides a browser based remote desktop that can act as a noVNC or RDP client (I think…?!).

One thing I’m wondering now is can this sort of thing be packaged using the “new”, (to my recollection, third(?) time of launching?!), Docker Application CNAB packaging format?

(For all their attempts to appeal to a wider audience, I think Docker keep missing a trick by not putting the Kitematic crew back together…)