https://github.com/zalari/docker-docker-cron

This is simple docker image including docker itself and cron for running docker with cron.
https://github.com/zalari/docker-docker-cron

Last synced: 4 months ago
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This is simple docker image including docker itself and cron for running docker with cron.

• Host: GitHub
• URL: https://github.com/zalari/docker-docker-cron
• Owner: zalari
• Created: 2020-01-15T14:36:12.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2020-01-16T11:27:23.000Z (over 6 years ago)
• Last Synced: 2025-03-12T15:50:41.053Z (over 1 year ago)
• Language: Dockerfile
• Size: 1.95 KB
• Stars: 0
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

          
# docker-cron

This is docker image for running cronjobs via a container. Its main purpose is, to trigger other docker containers via cron.

A possible use case are backups - you want to have regular backups for you dockerized application stack with neither setting up a cronjob **inside** your _database_ container nor setting up cron on the _host_.

With this container you can easily achieve this, by exposing the docker socket from the host to this container and setting up cronjobs via an _environment variable_.

## Usage

For setting up cronjobs, you have to pass an _environment variable_ `DOCKER_CRONTAB` to it - it can be _"multi-line", i.e. contain multiple entries by separating them with `\n`.

Although you can run arbitrary commands _inside_ this container, you likely want to run some sort of docker command _from inside_ the container communicating with the _outside_ docker daemon, for this you have to pass the docket socket to it.

```bash

docker run --rm -v /var/run/docker.sock:/var/run/docker.sock:ro \

       -e DOCKER_CRONTAB=\

       '*/5       *       *       *       *       docker info > /cron-env/docker-info.txt' \

       zalari/docker-cron

```

### with docker-compose

`docker-compose` is also conveniently provided in this image and this allows for adding cron functionality quite easily to your applications stacks:

```yaml

  # ...

  #this is a special service for exporting something to stdout

  #to use: docker-compose run --rm -T dump_db_out > db_dump/dump.sql

  dump_db_out:

    image: mysql:5

    # usually you would want some more params for mysqldump

    command: mysqldump

    depends_on:

      - db

   

  

  cron:

    image: zalari/docker-cron

    volumes:

      - ./docker-compose.yml:/cron-env/project/docker-compose.yml

      - ./db_dump:/cron-env/project/db_dump

      - /var/run/docker.sock:/var/run/docker.sock

    environment:

      - |

        DOCKER_CRONTAB=

        30       22       *       *       * cd /cron-env/project && docker-compose run --rm -T dump_db_out > db_dump/`date +"%m-%d-%y"`-project.sql

        30       22       *       *       * cd /cron-env/project/db_dump && find *.sql -mtime +30 -delete

  

```

## Hints

The image is based on the _rather latest_ `alpine` image and thus _only_ **BusyBox** and **ash** are available for cronjobs; if you need more tooling, simply base your image off this one.

You can also use the _default cronjobs_ from `alpine` if you either _add_ something or _bind-mount_ to the following dirs _in_ the container:

* `/etc/periodic/15min`

* `/etc/periodic/hourly`

* `/etc/periodic/daily`

* `/etc/periodic/weekly`

* `/etc/periodic/monthly`

For listing the actual `crontab` of the _running_ container, simply run: `docker exec container-name cat /var/spool/cron/crontabs/root`