A Cron Job manages time based Jobs, namely:
One CronJob object is like one line of a crontab (cron table) file. It runs a job periodically on a given schedule, written in Cron format.
For instructions on creating and working with cron jobs, and for an example of a spec file for a cron job, see Running automated tasks with cron jobs.
A cron job creates a job object about once per execution time of its schedule. We say “about” because there are certain circumstances where two jobs might be created, or no job might be created. We attempt to make these rare, but do not completely prevent them. Therefore, jobs should be idempotent.
startingDeadlineSeconds is set to a large value or left unset (the default)
concurrencyPolicy is set to
Allow, the jobs will always run
at least once.
Jobs may fail to run if the CronJob controller is not running or broken for a
span of time from before the start time of the CronJob to start time plus
startingDeadlineSeconds, or if the span covers multiple start times and
concurrencyPolicy does not allow concurrency.
For example, suppose a cron job is set to start at exactly
08:30:00 and its
startingDeadlineSeconds is set to 10, if the CronJob controller happens to
be down from
08:42:00, the job will not start.
Set a longer
startingDeadlineSeconds if starting later is better than not
starting at all.
The Cronjob is only responsible for creating Jobs that match its schedule, and the Job in turn is responsible for the management of the Pods it represents.