alpine

Docker image with cron (Alpine-based)

Docker image to run cron inside the Docker container

Adding cron jobs

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

# Dockerfile

FROM renskiy/cron:alpine

COPY crontabs /etc/crontabs

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:alpine 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:alpine start-cron \
    "\* \* \* \* \* env >> /var/log/cron.log 2>&1"

Special Environ variables

CRONTABS_DIR

This Environ variable let you provide custom crontabs directory location which will be used instead of default one (/etc/crontabs):

docker run --detach --name cron --env CRONTABS_DIR=/etc/my_app/crontabs renskiy/cron:alpine

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