robogeek/crond repository overview

This image allows you to run cron jobs in your Docker infrastructure. To keep things small, the image is built on Alpine, and therefore the crond is supplied by Busy Box. The default crond configuration is kept intact, though this can be overriden with a suitable Compose file configuration.

This image is based on discussion in a blog post: Scheduling background tasks using cron in a Docker container⁠

The corresponding Github repository is: https://github.com/robogeek/docker-cron⁠

Included in the image are the following packages

• mysql-client -- primarily to have mysqldump so that MySQL backup scripts can be supported
• less, gzip, rsync -- Generally useful tools to have available for writing cron jobs

The intended use is something like this:

version: '3.8'

services:

    crond:
        image: robogeek/crond
        networks:
            - wordpress-local_wpnet
        volumes:
            - ./hourly:/etc/periodic/hourly
            # This must be the path to where the Wordpress files are located
            - ../../wordpress-local/roots/html:/docroot
            - ./backups:/backups

networks:
    wordpress-local_wpnet:
        external: true

First, attach the container to any required networks so cron jobs can access desired services.

Second, override the directories that can contain cron jobs. The directories supported by the default Alpine Linux crond configuration are:

• /etc/periodic/15min - for jobs running every 15 minutes
• /etc/periodic/hourly - for jobs running every hour
• /etc/periodic/daily - for jobs running every day
• /etc/periodic/weekly - for jobs running every week

For whichever job frequency you desire, mount a directory into the container at the corresponding location. Any executable program (or shell script) in the directory is executed at the named frequency. It is important that executable programs not have a file extension, like .sh, because the run-parts program silently ignores such files.

Third, you mount into the container any directories you require for backups. For example to tar/gzip the files for a Wordpress container, that directory must be mounted into this container. Additionally a directory for storing any files can be mounted, like the /backups directory shown in this example.