bnutz/periodic-runner repository overview

⁠bnutz/periodic-runner

Periodically run a shell command on host machine on a cron schedule.

⁠DESCRIPTION:

This is primarily for host systems that don't have access to their own cron, or where the native cron is unreliable (like QNAP NAS's).

This container uses the pre-configured crond schedules in BusyBox to run its jobs (as discovered in this gist comment⁠)

bash-5.0# crontab -l
# do daily/weekly/monthly maintenance
# min   hour    day     month   weekday command
*/15    *       *       *       *       run-parts /etc/periodic/15min
0       *       *       *       *       run-parts /etc/periodic/hourly
0       2       *       *       *       run-parts /etc/periodic/daily
0       3       *       *       6       run-parts /etc/periodic/weekly
0       5       1       *       *       run-parts /etc/periodic/monthly

Handy if you just want to run a command at generic timeframes, and not too fussed at exactly when the command is run (e.g. for backup operations).

⁠PREREQUISITE:

• Need to be able to SSH into host server using private-key authentication.

⁠EXAMPLE USAGE:

docker run \
    --name=periodic-runner \
    --hostname=prunner \
    -e HOST_USERNAME="username" \
    -e COMMAND_DAILY="sh run_backup.sh" \
    -e COMMAND_HOURLY="ping www.example.com" \
    -v <path to ssh keys>:/root/.ssh \
    -d \
    bnutz/periodic-runner

This will set up a container that will SSH back into its own host system as username at the following periods:

• Once a day: Run a backup script located in the host user's home folder
• Once an hour: Ping the website www.example.com

⁠DOCKER PARAMETERS:

• Any unwanted COMMAND_* parameter can be left blank to not use that time interval.
• Only one command per interval is supported. To run multiple commands, place them all in a script on the host machine - and have the container execute the script instead.

⁠FIRST RUN:

The first time the container is run, you will need to generate the SSH keys that it will use to authenticate back into the host machine. This will be saved to the mapped SSH keys folder to allow the auth to continue working between container updates.

1. Start the Docker container with your target parameters configured.
2. Run on host to generate the keys inside the container:

   docker exec -it periodic-runner ssh-keygen
   

   Copy
   (Accept the default file location options, leave the passphrase empty)
3. Run on host to link the key inside the container to host:

   docker exec -it periodic-runner ./setup_key.sh
   

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4. Container should now be setup to trigger the commands on host at the specified intervals
5. To test a command immediately:

   docker exec -it periodic-runner ./run_command.sh "echo hello >> ~/test.txt"
   ls -l ~/
   

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   The test.txt greeting file now should appear in the home folder of your host machine.