crontab non executed in docker - docker

Question

I need to execute crontab inside docker container, so I created the following dockerfile:
FROM openjdk:11-oraclelinux8
RUN mkdir -p /opt/my-user/
RUN mkdir -p /opt/my-user/joblogs
RUN groupadd my-user && adduser my-user -g my-user
RUN chown -R my-user:my-user /opt/my-user/
RUN microdnf install yum
RUN yum -y update
RUN yum -y install cronie
RUN yum -y install vi
RUN yum -y install telnet
COPY talend /opt/my-user/
COPY entrypoint.sh /opt/my-user/
RUN chmod +x /opt/my-user/entrypoint.sh
RUN chmod +x /opt/my-user/ETLJob/ETLJob_run.sh
RUN chown -R my-user:my-user /opt/my-user/
RUN echo "*/2 * * * * /bin/sh /opt/my-user/ETLJob/ETLJob_run.sh >> /opt/my-user/joblogs/job.log 2>&1" >> /etc/cron.d/my-user-job
RUN chmod 0644 /etc/cron.d/my-user-job
RUN crontab -u my-user /etc/cron.d/my-user-job
RUN chmod u+s /usr/sbin/crond
USER my-user:my-user
ENTRYPOINT [ "/opt/my-user/entrypoint.sh" ]
My entrypoint.sh file is the following one:
#!/bin/bash
echo "Start cron"
crontab /etc/cron.d/diomedee-job
echo "cron started"
# Run forever
tail -f /dev/null
So far so good, the container is created successfully and when I go inside the container and I type crontab -l I see the crontab... but it is never executed
I can't figure out what I'm missing; any research I made didn't give me any clue
May you give me any tip?

Answer 1

Docker containers usually only host a single process. In your case, the tail process. The cron daemon isn't running.
Your comment 'cron started' seems to indicate that running crontab starts the daemon, but it doesn't.
Replace your tail -f /dev/null command with crond -f to run the cron daemon in the foreground and it should work.