Cron Container Starter

This is a simple Docker image that starts local Docker containers based on a cron schedule.

This is based off sillelien/tutum-cron which does the same job but inside Tutum.

Why would I want this?

This is quite useful to run backups or other scheduled jobs. Rather than having each of these jobs in a container with their own cron schedules, you can use this image to keep all schedule job configuration in one place.

How does it work?

The Docker socket must be provided to the container as a volume at /var/run/docker.sock. Through this, the container can issue a start command.

fcron is used to schedule this API call.

Building

Pull the repository and run: docker build -t jordancrawford/cron-container-starter ..

Running

To run you must:

provide /var/run/docker.sock as a volume
provide your cron schedules as environment variables. These must be of the format: CONTAINER_<container name to start>=<cron schedule>

Cron Schedules

See the fcron documentation or crontab-generator for help.

Docker Compose

The easiest way to run the image is within Docker Compose. Below an example Docker Compose file that runs a test container every minute.

cron-container-starter:
   container_name: cron-container-starter
   image: jordancrawford/cron-container-starter
   restart: always
   # Don't take a large portion of memory or CPU shares.
   cpu_shares: 128
   mem_limit: 64m
   # Setup container start rules.
   environment:
    CONTAINER_test: '* * * * *'
   # Setup the Docker socket as a volume so the container can control Docker.
   volumes:
    - /var/run/docker.sock:/var/run/docker.sock
test:
   image: alpine
   container_name: test
   command: 'echo On Schedule'