A lightweight cron container, which allows crontabs to be specified using environment variables.

This allows for rapid prototyping and development of cron jobs, especially when using docker-compose.

Configure the cron container using environment variables. Each environment variable named with the prefix CRON_D_ is linked into /etc/cron.d/, the filename of which will be the environment variables name; e.g.

docker run \
  -e "CRON_D_HELLO_WORLD=* * * * * root echo Hello World from \$(whoami) | logger\n" \
  nickbreen/cron

Will create a file /etc/cron.d/CRON_D_HELLO_WORLD.

cron jobs are not logged per-se. Instead, if an MTA is available, their output is emailed to the owner of the crontab. Otherwise, the job should explicitly pipe stdout and stderr (with 2>&1) to logger.

This example job echos the value of $HELLO_WORLD or exits with an error and message if it's undefined.

docker run \
  -e 'HELLO_WORLD=Hello World!' \
  -e "CRON_D_HELLO=* *    * * *    root . /etc/container_environment.sh; echo \${HELLO_WORLD:?variable not set} 2>&1 | logger\n" \
  nickbreen/cron:v2.0.0