Mar 27, 2024

CronJob 总结

cgxxv

kubernetes

374 Words | 1 Minute, 42 Seconds

2024-03-27 10:30 +0800

v1.21 stable

CronJob used for performing regular scheduled actions such as backups, report generation…

Schedule syntax

# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of the month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday)
# │ │ │ │ │                                   OR sun, mon, tue, wed, thu, fri, sat
# │ │ │ │ │
# │ │ │ │ │
# * * * * *

Deadline for delayed Job start

spec.startingDeadlineSeconds

  • After missing the deadline, the CronJob skips that instance of the job (future occurrences are still scheduled)
  • For Jobs that miss their configured deadline, Kubernetes treats theme as failed Jobs. No startingDeadlineSeconds, no deadline for this CronJob.
  • If the spec.startingDeadlineSeconds field is set, the CronJobController measures the time between a Job is expected to be created and now. If the difference is higher than that limit, it will ship this execution.

注意：如果 startingDeadlineSeconds 的设置值低于 10 秒钟，CronJob 可能无法被调度。 这是因为 CronJob 控制器每 10 秒钟执行一次检查。

Concurrency policy

spec.concurrencyPolicy specifies how to treat concurrent executions of a Job that is created.

  • Allow (default): allow concurrently run.
  • Forbid: Do not allow concurrent runs.
  • Replace: old and new Job may run at the same time, the new one will replace the old one.

Schedule suspension

spec.suspend = true for this case. When spec.suspend changes from true to false on an existing CronJob without a spec.startingDeadlineSeconds, the missed Jobs are scheduled immediately.

Jobs history limits

spec.successfulJobsHistoryLimit = 3, spec.failedJobsHistoryLimit = 1. These fields specify how many completed and failed jobs should be kept.

Time zones (v1.27 stable)

spec.timeZone instructs Kubernetes to interpret the schedule relative to Coordinated Universal Time.

CronJob limitations

  • Unsupported TimeZone specification

    CRON_TZ or TZ is not officially supported, and starting with v1.29, Kubernetes will fail to create the resource with a validation error.

  • Modify a CronJob

    Modify an existing CronJob will have no effect to existing Jobs, and new Jobs will take effect.

  • Job creation

    The Jobs that user defined are idempotent. If the scheduled time from last time until now, the missed count > 100, then new Job will not be created from now.

See Also