Hi,
i've tried to build the image adding your line like:
...
RUN apt-get update \
&& apt-get install --no-install-recommends -y xmlstarlet \
&& rm -rf /var/lib/apt/lists/* \
&& pip install gunicorn==20.0.4 \
&& pip install -r requirements.txt \
&& pip install matplotlib==3.3.3
...
And i've built it with:
docker build -t my-knowage-python-docker . --build-arg KNOWAGE_APP_BRANCH=master
And finally I've ran:
docker run -ti --rm --entrypoint sh my-knowage-python-docker -c "pip freeze"
And I was able to see matplotlib correctly installed:
[user@host]$ docker run -ti --rm --entrypoint sh my-knowage-python-docker -c "pip freeze"
WARNING: The directory '/home/knowage/.cache/pip' or its parent directory is not owned or is not writable by the current user. The cache has been disabled. Check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
bokeh==1.3.4
certifi==2020.12.5
chardet==3.0.4
click==7.1.2
cycler==0.10.0
Flask==1.1.1
Flask-Cors==3.0.8
gunicorn==20.0.4
idna==2.8
itsdangerous==1.1.0
Jinja2==2.11.2
kiwisolver==1.3.1
MarkupSafe==1.1.1
matplotlib==3.3.3
numpy==1.19.4
packaging==20.7
pandas==0.25.1
Pillow==8.0.1
pybase64==1.0.1
PyJWT==1.7.1
pyparsing==2.4.7
python-dateutil==2.8.1
pytz==2020.4
PyYAML==5.3.1
requests==2.22.0
six==1.15.0
tornado==6.0.3
urllib3==1.25.11
Werkzeug==1.0.1
Could you confirm to me that you followed those steps to build your custom image?