debugging containerised python web app

Question

I have made this first docker container, and it works as per the Dockerfile.

FROM python:3.5-slim

RUN apt-get update && \
    apt-get -y install gcc mono-mcs && \
        apt-get -y install vim && \
        apt-get -y install nano && \
            rm -rf /var/lib/apt/lists/*

RUN mkdir -p /statics/js

VOLUME ["/statics/"]

WORKDIR /statics/js

COPY requirements.txt /opt/requirements.txt

RUN pip install -r /opt/requirements.txt

EXPOSE 8080

CMD ["python", "/statics/js/app.py"]

after running this command:

docker run -it -p 8080:8080 -v ~/Development/my-Docker-builds/pythonReact/statics/:/statics/ -d ciasto/pythonreact:v2

and when I open the page localhost:8080 i get error:

A server error occurred.  Please contact the administrator.

but if I run this application normally, i.e. not containerised directly on my host machine: it works fine.

So I want to know what is causing server error. How do I debug a python app that runs via container to know what is causing it to not work. or what am I doing wrong.

Answer 1

Mainly, this:

config.paths['static_files'] = 'statics'

Should be:

config.paths['static_files'] = '/statics'

---

I've got your application up and running with your 'Hello World'

Did these changes:

1) The mentioned config.paths['static_files'] = '/statics'

2) This Dockerfile (removed VOLUME)

FROM python:3.5-slim

RUN apt-get update && \
    apt-get -y install gcc mono-mcs && \
    apt-get -y install vim && \
    apt-get -y install nano && \
        rm -rf /var/lib/apt/lists/*

COPY requirements.txt /opt/requirements.txt

RUN pip install -r /opt/requirements.txt

COPY ./statics/ /statics/
COPY app.py /app/app.py
WORKDIR /statics/js

EXPOSE 8080

CMD ["python", "/app/app.py"]

3) Moved the non-static app.py to a proper place: root of the project.

4) Run with: docker build . -t pyapp, then docker run -p 8080:8080 -it pyapp

You should see Serving on port 8080... from terminal output. And Hello World in browser.

I've forked your Github project and did a pull-request.

---

Edit:

If you need make changes when you develop, run the container with a volume to override the app that is packed in the image. For example:

docker run -v ./static/js/:/static/js -p 8080:8080 -it pyapp

You can have as many volumes as you want, but the app is already packed in the image and ready to push somewhere.