linux - How to run a cron job inside a docker container

Question

I tried to run a cron job inside a docker container but nothing works for me.
My container has only cron.daily and cron.weekly files.
crontab,cron.d,cron.hourly are absent in my container.
crontab -e is also not working.
My container runs with /bin/bash.

Answer 1

Here is how I run one of my cron containers.

Dockerfile:

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!"

Build like so

docker build -t mycron .

Run like so

docker run -d mycron

Add your own scripts and edit the crontab.txt and just build the image and run. Since it is based on alpine, the image is super small.