docker root crontab job not executing

Question

I have an Ubuntu 14.04 docker image that I want to schedule a python script within to execute every minute. My DockerFile contains CMD ["cron","-f"] in order to start the cron daemon. The crontab entry looks like this:

0,1 * * * * root python /opt/com.org.project/main.py >> /opt/com.org.project/var/log/cron.log

/opt/com.org.project/main.py is completely accessible and owned by root and has 744 privileges set; so can be executed.

Nothing is showing up in my /opt/com.org.project/var/log/cron.log file, nor /var/log/cron.log. Yet ps aux | grep cron shows cron -f running at PID 1.

What am I missing? Why is my cron job not running within the container?

Here are my DockerFile contents as requested:

FROM ubuntu

# Update the os and install the dependencies needed for the container
RUN apt-get update \
&& apt-get install -y \
nano \
python \
python-setuptools \
python-dev \
xvfb \
firefox

# Install PIP for python package management
RUN easy_install pip

CMD ["cron", "-f"]

Answer 1

Why use cron? Just write a shell script like this:

#!/bin/bash
while true; do
  python /opt/com.org.project/main.py >> /opt/com.org.project/var/log/cron.log
  sleep 60
done

Then just set it as entrypoint.

ENTRYPOINT ["/bin/bash", "/loop_main.sh" ]

Answer 2

Where did you use crontab -e? On the host running docker or in the container itself?

I can't see that you are adding an crontab entry in the dockerfile you provided. I recommend you to add an external crontab file like this:

ADD crontabfile /app/crontab
RUN crontab /app/crontab
CMD ["cron", "-f"]

The file crontabfile has to be located next to Dockerfile.

image_folder
|
|- Dockerfile
|- crontabfile

Example content of crontabfile:

# m h  dom mon dow   command
30  4 * * * /app/myscript.py