Xtykutl

I'm having a strange issue when trying to run a Python script via Crontab within a Docker container. Here's the setup.

I have a Dockerfile like this:

FROM python:3-onbuild



# Install cron and dependencies

RUN apt-get update && apt-get -y install cron



# Add crontab file in the cron directory

ADD crontab /etc/cron.d/simple-cron

WORKDIR /src

COPY . /src



# Give execution rights on the cron job

RUN chmod 0644 /etc/cron.d/simple-cron

RUN chmod 777 /usr/local/lib/python3.6/site-packages



# Create the log file to be able to run tail

RUN touch /var/log/cron.log



# Run the command on container startup

CMD ["cron", "-f"]

And a crontab file like this:

* * * * * root python /src/test.py > /proc/1/fd/1 2>/proc/1/fd/2

This executes correctly with no problems when I start the container. The first line of my Python file is import redis, which causes the script to fail, saying that the module cannot be found.

The interesting thing is that when I manually execute docker exec -it [container_name] python test.py, everything works exactly as expected.

What could be the issue here? I'm thinking that the requirements file isn't being installed to the right location?

With python in docker I definitely find it helpful to use a vendoring tool. Instead of copying the local site-packages, run a script or series of RUN commands which:

1. Establish the virtualenv


2. Activate it


3. call pip install -r requirements.txt
   

Here's an example from a script I use in dev:

pip3 install virtualenv;

virtualenv --no-site-packages --python=python3.6 app;

virtualenv --relocatable app;

source ./app/bin/activate;

pip3 install -r requirements.txt;