[FEATURE REQUEST] random/N for salt.states.cron

[dseomn]

Describe the solution you'd like
salt.states.cron currently supports values like minute: '*/5' to run every 5 minutes. If I understand correctly, that runs on minutes 0, 5, 10, etc., right? There's also support for minute: 'random' to run on a random minute. It would be nice to have the combination of those two features so something like minute: 'random/5' would run every 5 minutes, starting on a random minute between 0 and 4.

Describe alternatives you've considered
I'm not aware of any other easy way to spread out cron jobs that run every N minutes/hours/etc. It is possible for a cron job to sleep for a random amount of time before doing anything else though.

[leeclemens]

On Fedora 34 random/5 does not appear to be a valid format. I ran 0-6 for testing and they never printed anything, but */5 worked as expected.

Test

/etc/crontab

*/5 * * * *	root	echo "*/5: $(date)" >> /tmp/crontest
0/5 * * * *	root	echo "0/5: $(date)" >> /tmp/crontest
1/5 * * * *	root	echo "1/5: $(date)" >> /tmp/crontest
2/5 * * * *	root	echo "2/5: $(date)" >> /tmp/crontest
3/5 * * * *	root	echo "3/5: $(date)" >> /tmp/crontest
4/5 * * * *	root	echo "4/5: $(date)" >> /tmp/crontest
5/5 * * * *	root	echo "5/5: $(date)" >> /tmp/crontest
6/5 * * * *	root	echo "6/5: $(date)" >> /tmp/crontest

/tmp/crontest

*/5: Thu Jul 22 03:15:01 PM EDT 2021
*/5: Thu Jul 22 03:20:01 PM EDT 2021
*/5: Thu Jul 22 03:25:01 PM EDT 2021

crond[3392]: (CRON) bad minute (/etc/crontab)

[dwoz]

Seems like this could be a useful feature. I do wonder how far off of upstream cron implementations we'd be headed. I know some cron implementations have the ability to add random delay to jobs. Adding support for this might accomplish what you are after.

[dseomn]

@leeclemens Thanks for looking into that. I think it might work to do 0-59/5, 1-59/5, etc. If that doesn't work, then I think the other way to implement it is 0,5,10,..., 1,6,11,..., etc.

@dwoz Makes sense, and thanks, I'll look at some other cron implementations.

[leeclemens]

@dseomn having salt extrapolate those combinations would be my next thought based on what I've seen. May get a little cumbersome, so perhaps there's a more elegant solution.

I saw some notations like */5+2 as well, but I'm not sure what systems use it.

[dseomn]

https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_filters.html#random-items-or-numbers has another idea for how to implement this. I haven't tested this yet, but I think using https://docs.saltproject.io/en/latest/ref/modules/all/salt.modules.mod_random.html#salt.modules.mod_random.rand_int could work something like:

minute: {{ salt['random.rand_int'](0, 4, seed=grains.id + ':some-id-for-this-specific-cron-job') }}}-59/5