Docker for GUI-based environments?

Question

Problem

I have a set of client machines that are a part of an enterprise web application. Each machine runs identical software, which is a PyQT-base

Answer 1

SOLVED - PyQt5-GUI in Docker Container:

Enable Qt-Debug $ export QT_DEBUG_PLUGINS=1 ==> reproduce error ==> re/install the No such file or directory-library listed in debug message ==> repeat!

I also could not run PyQt5-GUI-app in a Docker container without receiving errors & first read all the posts that it would not be possible to run Qt in Docker containers. But I could solve it (at least for me)...

System

I am running my PyQt5-application in a Docker container with shared /tmp/.X11-unix/ socket and display for GUI visualization:

$ nividia-docker run --interactive --tty --env DISPLAY=$DISPLAY --volume /tmp/.X11-unix/:/tmp/.X11-unix/ 

Error

Initializing PyQt5.QtWidgets.QApplication always led to following error:

Type "help", "copyright", "credits" or "license" for more information.
>>> from PyQt5.QtWidgets import QApplication
>>> app = QApplication([])
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb.

Aborted (core dumped)

In PyCharm Debug mode the error returned:

Process finished with exit code 134 (interrupted by signal 6: SIGABRT)

Solution

General method:

• set Qt-debug environement variable in docker container terminal:

   $ export QT_DEBUG_PLUGINS=1

• reproduce error in the docker terminal (or in the IDE), e.g.:

$ python
Python 3.6.8 |Anaconda, Inc.| (default, Dec 30 2018, 01:22:34) 
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

>>> 
KeyboardInterrupt
>>> from PyQt5.QtWidgets import QApplication, QLabel
>>> app = QApplication([])

• read debug messages printed to the terminal, e.g.:

QFactoryLoader::QFactoryLoader() checking directory path "/conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms/libqeglfs.so"
Found metadata in lib /conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms/libqeglfs.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "eglfs"
        ]
    },
...
...
...
Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/conda/envs/rapids/bin/platforms" ...
Cannot load library /conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (libxkbcommon-x11.so.0: cannot open shared object file: No such file or directory)
QLibraryPrivate::loadPlugin failed on "/conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so" : "Cannot load library /conda/envs/rapids/lib/python3.6/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (libxkbcommon-x11.so.0: cannot open shared object file: No such file or directory)"
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb.

Aborted (core dumped)

• find the .so.* and -packages, here e.g. libxkbcommon-x11.so.0 and libxcb. Then re/install the corresponding packages/libraries (finding the packages works with apt-file --package-only search or conda/pip search ...). In my case the following libs were required:

### lib no.1 ###
$ sudo conda install --name  --force-reinstall libxcb    # or pip install ...
### lib no. 2 ###
$ apt-file --package-only search libxkbcommon-x11.so.0
libxkbcommon-x11-0
$ sudo apt install libxkbcommon-x11-0 

After repeating this process for all sequentially reproduced debug messages and installing the 2 libs I can now run PyQt5-apps from inside the Docker container on my local machine desktop.