How do I run a cron job inside a docker container

Question

I am trying to run a cron job inside a docker container but it’s not working out for me.

My container has only cron. daily and cron.weekly file

crontab, cron.d, cron.hourly ... are not present in my container

I have tried to use crontab -e  but it’s also not working

The container which I am using runs with /bin/bash

Answer 1

If you can SSH into your server and it’s running a distro of Linux that has cron available then you’re good to go. If you spin up a server on any other major cloud provider and install Ubuntu you’re all set. Cron will be available to you on the Docker host. Done deal. Then you can just run whatever task you need.

Answer 2

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.

Answer 3

Running a cron job from inside a container is not recommended. A better option is to run it from the host itself.

Answer 4

In the same folder as your Dockerfile, create a file called crontab:

* * * * * /file.sh
# Mandatory blank line

Then add the following to your Dockerfile:

COPY crontab /etc/cron.d/work
RUN chmod 0644 /etc/cron.d/work
RUN service cron start

Rebuild the Docker image, and you’re all set!

Answer 5

Try something like this:

FROM ubuntu:latest

# Install cron
RUN apt-get -y install cron

# Create the log file to be able to run tail
RUN touch /var/log/cron.log

# Setup cron job
RUN (crontab -l ; echo "* * * * * echo "Hello world" >> /var/log/cron.log") | crontab

# Run the command on container startup
CMD cron && tail -f /var/log/cron.log