How to control interval between kubernetes cronjobs (i.e. cooldown period after completion)

If I set up a kubernetes cronjob with for example

spec:
  schedule: "*/5 * * * *"
  concurrencyPolicy: Forbid

then it will create a job every 5 minutes.

However if the job takes e.g. 4 minutes, then it will create another job 1 minute after the previous job completed.

Is there a way to make it create a job every 5 minutes after the previous job finished?

You might say; just make the schedule */9 * * * * to account for the 4 minutes the job takes, but the job might not be predictable like that.

Solution

Unfortunately there is no possibility within Kubernetes CronJob to specify a situation when the timer starts (for example 5 minutes) after a job is completed.

A word about cron:

The software utility cron is a time-based job scheduler in Unix-like computer operating systems. Users that set up and maintain software environments use cron to schedule jobs (commands or shell scripts) to run periodically at fixed times, dates, or intervals.

-- Wikipedia.org: Cron

The behavior of your CronJob within Kubernetes environment can be modified by:

As said Schedule in spec definition
```
  schedule: "*/5 * * * *"
```
startingDeadline field that is optional and it describe a deadline in seconds for starting a job. If it doesn't start in that time period it will be counted as failed. After a 100 missed schedules it will no longer be scheduled.
Concurrency policy that will specify how concurrent executions of the same Job are going to be handled:
- Allow - concurrency will be allowed
- Forbid - if previous Job wasn't finished the new one will be skipped
- Replace - current Job will be replaced with a new one
Suspend parameter if it is set to true, all subsequent executions are suspended. This setting does not apply to already started executions.

You could refer to official documentation: CronJobs

As it's unknown what type of Job you want to run you could try to:

Write a shell script in type of:

    while true
    do
      HERE_RUN_YOUR_JOB_AND_WAIT_FOR_COMPLETION.sh
      sleep 300 # ( 5 * 60 seconds ) 
    done

Create an image that mimics usage of above script and use it as pod in Kubernetes.
Try to get logs from this pod if it's necessary as described here

Another way would be to create a pod that could connect to Kubernetes API.

Take a look on additional resources about Jobs:

Please let me know if you have any questions to that.