bobby4k / crond

Another crontab for executing recurring tasks

Along Crond: Standalone Task Management

• Another crontab for executing recurring tasks
• Only one task with the same name can exist at a given time

Dependencies

• bash
  • sleep usleep bc cut
• php-cli

Usage

# See example.ini
vim mytasks.ini
chmod +x crond.sh
crond.sh start mytasks.ini

Background

• Single Machine, Multiple Applications
  • Due to centralized deployment, several projects (php/slim, php/webman, go/somer, go/ginping, python/kingpin X2) are deployed on the same machine. Of course, not all of them are docker containers; the tasks come in various flavors.
  • Why not separate deployments? The machine has 32 cores and 64GB memory, which might not be attainable in a cloud service.
• Insufficiency of crontab
  • Cron does not care if the previous run of the same task has completed when a new instance starts. When a task starts, I want the previous one to have completed and exited.
  • Crontab has another issue. When NTP synchronized time exceeds 1 second, the scheduled tasks will no longer run.
• Solution from a Decade Ago
  • Perhaps supervisor is more suitable, but the configuration is relatively cumbersome.
  • Digging out a solution from ten years ago, utilizing bash while loop to control the loop, with some modifications it works fine. Let's go with it.