Oban Periodic (CRON) Job multi node question

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1

Hey,

I have been using quantum for cron kind of jobs in a project, and when 2 instances of this project were running the jobs were running 2 which is not surprising. I know this could be solved(highlander etc.) but I have been eyeing with Oban for a while.

This is a quote from their readme:

Periodic (CRON) Jobs — Automatically enqueue jobs on a cron-like schedule. Duplicate jobs are never enqueued, no matter how many nodes you’re running.

Does this mean that if I have 2 instances of the same project running while connected to 1 database I would not see these jobs duplicated anymore without doing any additional work(other than setting up Oban and migrating the jobs)?

Thank you

2

Yes. That’s exactly what it means :slightly_smiling_face:

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3

Hi,

What are the criteria for duplicates in case of the Oban.Plugins.Cron? Would the following crontab entries be handled as duplicates or two distinct jobs?

{"0 * * * *", MyApp.HourlyWorker, args: %{custom: "arg"}},

{"0 * * * *", MyApp.HourlyWorker, args: %{custom: "some other value"}},

My use case would be to change my worker’s arguments with a new release.

Thank you in advance.

4

That’s a perfectly fine change. Those would be different jobs because the args are different.

No unique checks would apply anyhow, because it’s inserting those jobs an hour apart and the default unique period is only for 59 seconds.

5

Thanks. Just to be sure I understand it correctly here’s the sequence I get out of this:

  1. app starts with a single crontab entry with hourly worker args: %{custom: "arg"}
  2. cron plugin adds a job instance with args: %{custom: "arg"} scheduled to run in an hour
  3. app is shut down before the job ran
  4. app starts with a single crontab entry but now with hourly worker args: %{custom: "some other value"}
  5. cron plugin adds a job instance with args: %{custom: "some other value"} scheduled to run one hour from now
  6. one hour after step 2 the first job (with args: %{custom: "arg"}) is executed, no new instance is added anymore
  7. one hour after step 5 the second job (with args: %{custom: "some other value"}) is executed
  8. cron plugin adds a job instance with args: %{custom: "some other value"} scheduled to run one hour from now
6

That’s not quite right.

Cron doesn’t schedule jobs to run later, it inserts them right at the time they’re supposed to run (at the top of the minute). Whichever args are set in your code when the plugin runs is what will be inserted.

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7

Ah, makes sense. Thanks a lot for your time and this great project.

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