justb4/cron repository overview

⁠docker-cron

Dockerfile and scripts for creating image to use cron. Based on Alpine Linux. Installed packages: dcron docker docker-compose and ca-certificates.

Allows to execute commands in other Docker images.

Inspired from: https://github.com/xordiv/docker-alpine-cron⁠ - mainly added Docker tools.

It installs and uses "Dillon's Cron" dcron, via APK: http://www.jimpryor.net/linux/dcron.html⁠

⁠Environment variables:

• CRON_STRINGS - strings with cron jobs. Use "\n" for newline (Default: undefined)
• CRON_TAIL - if defined cron log file will read to stdout by tail (Default: undefined)
• CRON_DEBUG_LEVEL - set cron daemon loglevel: emerg|alert|crit|err|warning|notice|info|debug (Default: notice)

By default cron daemon runs in the foreground unless CRON_TAIL is set.

⁠Cron files

• /etc/cron.d - place to mount custom crontab files

When the image is run, files in /etc/cron.d will be copied to /var/spool/cron/crontab.
If CRON_STRINGS is defined the entry script⁠ creates the file /var/spool/cron/crontab/CRON_STRINGS.

⁠Log files

By default placed in /var/log/cron.log

⁠Simple usage:

docker run --name="cron-sample" -d \
-v /path/to/app/conf/crontabs:/etc/cron.d \       
-v /path/to/app/scripts:/scripts \
justb4/cron

⁠With scripts and CRON_STRINGS

docker run --name="cron-sample" -d \
-e 'CRON_STRINGS=* * * * * /scripts/myapp-script.sh'
-v /path/to/app/scripts:/scripts \
justb4/cron

⁠Print date to file every minute

docker run --name="cron-sample" -d \
-e 'CRON_STRINGS=* * * * * echo "date=$(date) > /tmp/dates.txt'
justb4/cron

⁠Docker Compose

See complete example in test dir⁠. This is the preferred way of running. Also shows how to use Docker client commands.