Here is how I run one of my cron containers. Docker file:
FROM alpine:3.3
ADD crontab.txt /crontab.txt
ADD script.sh /script.sh
COPY entry.sh /entry.sh
RUN chmod 755 /script.sh /entry.sh
RUN /usr/bin/crontab /crontab.txt
CMD ["/entry.sh"]
crontab.txt
*/30 * * * * /script.sh >> /var/log/script.log
entry.sh
#!/bin/sh
# start cron
/usr/sbin/crond -f -l 8
script.sh
#!/bin/sh
# code goes here.
echo "This is a script, run by cron!"
Execute this command to build
docker build -t mycron .
Execute this command to run
docker run -d mycron
Just add your own scripts and edit the crontab.txt and just build the image and run.I hope it will resolve all your query.