blacklabelops/cronut repository overview

⁠Cronut - Delicious Docker Cron

The delicious cron software solution for your Docker environment.

Cronut is a cron daemon for Docker environments. Finally, dynamically executing cron on containers.

⁠Why Cronut?

Everybody needs cron jobs! Cron jobs on containers containing your scripts!

Example:

Firstly, start Cronut:

$ docker run -d --name cronut \
    -v /var/run/docker.sock:/var/run/docker.sock \
    blacklabelops/cronut

Secondly, start any container with cron jobs and keep it running:

$ docker run -d \
    -e "CRONJOB1NAME=Job1" \
    -e "CRONJOB1CRON=* * * * *" \
    -e 'CRONJOB1COMMAND=echo "Hello World!"' \
    busybox sh -c "while sleep 600; do :; done"

⁠Job Configuration

You can define an arbitrary amount of jobs. That's why jobs have to defined by enumerated environment variables starting from index 1, e.g. CRONJOB1, CRONJOB2, CRONJOB3 and so on.

Job settings are defined by configuration fields and the jobs can be defined using the following fields:

• NAME: (Required) A unique job name, must be unique among all container's jobs.
• CRON: (Required) The cron schedule. Specifics and syntax can be found here Wikipedia - Cron⁠
• COMMAND: (Required) The command to be executed.
• PRE_COMMAND: (Optional) This command to be executed before the actual command.
• POST_COMMAND: (Optional) This command to be executed after the actual command.
• SHELL_COMMAND: Optional) The shell command. Example: /bin/sh -c or /bin/bash -c.
• EXECUTION: (Optional) The execution mode. Possible values parallel or sequential. A single job will be either executes strictly sequential or multiple instances of the same job can run in parallel. Default is: sequential.
• ON_ERROR: (Optional) The error mode. Possible values stop or continue. A single job will be either executed continuesly despite of errors or will not be scheduled anymore after an error occured. Default is: continue.

Setting a job configuration field:

All fields are configured as environment variables. The environment variable are preceeded by the enumerated jobs prefix, e.g. CRONJOB1, CRONJOB2, CRONJOB3:

Example minimal job configuration:

$ docker run -d \
    -e "CRONJOB1NAME=Job1" \
    -e "CRONJOB1CRON=* * * * *" \
    -e 'CRONJOB1COMMAND=echo "Hello World"' \
    your-image

Example full job configuration:

$ docker run -d --name cronut \
    -e "CRONJOB1NAME=Job1" \
    -e "CRONJOB1CRON=* * * * *" \
    -e 'CRONJOB1PRE_COMMAND=echo "Hello World - Pre"' \
    -e 'CRONJOB1COMMAND=echo "Hello World"' \
    -e 'CRONJOB1POST_COMMAND=echo "Hello World - Post"' \
    -e "CRONJOB1SHELL_COMMAND=/bin/bash -c" \
    -e "CRONJOB1EXECUTION=sequential" \
    -e "CRONJOB1ON_ERROR=continue" \
    your-image

⁠Command Line Client

This image includes a command line interface (cli). The cli can be run against local or remote cronut server.

Supported Commands:

Configuration:

• CRONUT_BASE_URL: The server's base url. Default: http://localhost:8080.

Usage:

$ docker exec your_cronut_container cronut list

⁠Changing The User

You can specify linux group id and user id for the scheduler.

Example:

$ docker run -d --name cronut \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -e "CRONUT_GID=1000" \
    -e "CRONUT_UID=1000" \
    blacklabelops/cronut

⁠Debug Mode

Set environment variable DEBUG to value true to activate Cronut in debug mode.

Example:

$ docker run -d --name cronut \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -e "DEBUG=true" \
    blacklabelops/cronut

⁠References

• Crow Cron Web Scheduler⁠