garrcomm/crontainer repository overview

⁠Crontainer

This container can execute scheduled tasks.

Scheduled tasks can be;

• Webhook calls to all kinds of web services.
  For this, curl --silent --request [method] --location [url] is used.
• Executables in an active container; if the volume /run/docker.sock is mounted correctly, it's also possible to execute jobs in other containers.
  To do this, docker container exec --tty [container] [command] is used.
• Executables in an image; if the volume /run/docker.sock is mounted correctly, it's also possible to execute jobs in other containers.
  To do this, docker container run --rm --tty [image] [command] is used.
• Remote ssh executions with a private key exchange.
  To do this, ssh -T -o StrictHostKeyChecking=no -o IdentitiesOnly=yes -o UserKnownHostsFile=~/known_hosts -i ~/id_rsa "user@hostname" [command] could be executed.

⁠Installation instructions

There are two easy ways to start Crontainer. By command line and with a Docker Compose file.

In both examples you'll see a few variables that can be changed to your needs:

• The volume mount from /home/user/crontainer_data to /etc/crontainer can be replaced to a folder on the host system where Crontainer can store its persistent data.
• The volume mount /run/docker.sock to /run/docker.sock is used to execute jobs in other Docker containers. Depending on your host configuration, it's also possible this can be replaced to /run/user/$(id -u)/docker/docker.sock:/run/docker.sock or something completely different.
  As long as it points to the docker.sock on the host system, it'll be fine.

At the first run, you'll be asked for a new username and password.

Start Crontainer by command line

docker container run --detach --restart always -p '80:80' --name crontainer \
    --volume '/run/docker.sock:/run/docker.sock' \
    --volume '/home/user/crontainer_data:/etc/crontainer' \
    garrcomm/crontainer:latest

Start Crontainer with a compose file

services:
  crontainer:
    image: garrcomm/crontainer:latest
    volumes:
      # By making a volume of the Docker socket, we can access other containers to run jobs inside those.
      - /run/docker.sock:/run/docker.sock
      # This volume defines where to store the crontab.db and htpasswd file.
      - /home/user/crontainer_data:/etc/crontainer
    ports:
      - "80:80"
    restart: always

⁠UNIX cron format

The cron format contains 5 parts:

⁠Always matches

When using an asterisk (*) will cause it to match every value.

⁠Lists

Multiple values can be comma separated. So 1,2,3 will match the values 1 to 3, but nothing else.
The same works for months and days, jan,feb matches the first two months and mon,wed matches each Monday and Wednesday.

⁠Ranges

It's also possible to provide a range by separating two values with a dash (-). So 1-6 matches all values from 1 to 6.
The same works for months and days, so jun-sep will match all months from June to September and mon-fri matches all working days.

⁠Step values

Step values are two values separated by a slash (/).

Depending on the value before the slash, the following happens if we apply it to the minute value:

• */5 Matches every five minutes, so 0, 5, 10, 15, 20, etc.
• 3/2 Matches every two minutes from the 3rd minute on, so 3, 5, 7, 9, 11 etc.
• 8-20/2 Matches every two minutes in range 8 to 20, so 8, 10, 12, 14, 16, 18, 20.