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.
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Answer 1

crond works well with tiny on Alpine

RUN apk add --no-cache tini

ENTRYPOINT ["/sbin/tini", "--"]
CMD ["/usr/sbin/crond", "-f"]

but should not be run as container main process (PID 1) because of zombie reaping problem and issues with signal handling. See this Docker PR and this blog post for details.