pythoncelery

Celery, run task once at a specified time


How can I run a celery task at a given time, but only once?

I read the documentation and couldn't find any example of this.


Solution

  • If you insist on using Celery

    To run a task at a specified time, in Celery you would normally use a periodic task, which conventionally is a recurring task.

    However, you may create a periodic task with a very specific schedule and condition that happens only once so effectively it runs only once.

    Unfortunately we can only specify so much, e.g. we can specify hour, minute, day_of_month and month_of_year but we can't specify year

    However with that, your task would run at most 1 time for per year, so below are some workarounds:

    Unschedule it after it is ran

    It should be relatively easy to unschedule it once it is ran (you have 1 year to do so!)

    Use a "DONE" flag when the task completes

    With a flag written somewhere (disk or DB), you can first check if the task has run before or not, i.e. if done: exit

    Exit if not proper year or you want to be safe, just add code into the task that checks the year, e.g. if year != 2017: exit.

    Simple cron/Os level scheduler works too

    You may also skip Celery altogether and use some OS level facility like cron for UNIX-like systems, more on that here.

    The general idea remains the same.