renskiy/cron repository overview

⁠Docker image with cron (Debian-based)

Docker image to run cron inside the Docker container

⁠Adding cron jobs

Suppose you have folder cron.d with your cron scripts. The only thing you have to do is copying this folder into the Docker image:

# Dockerfile

FROM renskiy/cron:debian

COPY cron.d /etc/cron.d

Then build and create container:

docker build --tag my_cron .
docker run --detach --name cron my_cron

⁠Logs

To view logs use Docker logs⁠ command:

docker logs --follow cron

All you cron scripts should write logs to /var/log/cron.log. Otherwise you won't be able to view any log using this way.

⁠Passing cron jobs by arguments

Additionally you can pass any cron job by argument(s) using custom start-cron command at the moment of container creation (providing optional user with -u/--user option):

docker run --detach --name cron renskiy/cron:debian start-cron --user www-data \
    "0 1 \* \* \* echo '01:00 AM' >> /var/log/cron.log 2>&1" \
    "0 0 1 1 \* echo 'Happy New Year!!' >> /var/log/cron.log 2>&1"

⁠Environ variables

Almost any environ variable you passed to the Docker will be visible to your cron scripts. With the exception of $SHELL, $PATH, $PWD, $USER, etc.

docker run --tty --rm --interactive --env MY_VAR=foo renskiy/cron:debian start-cron \
    "\* \* \* \* \* env >> /var/log/cron.log 2>&1"

⁠Special Environ variables

⁠CRON_PATH

This Environ variable let you provide custom directory for your cron.d scripts which will be placed instead of default /etc/cron.d:

docker run --detach --name cron --env CRON_PATH=/etc/my_app/cron.d renskiy/cron:debian

This may be very useful when you create more then one Docker container from a single image with different cron jobs per container.