docs/apache-airflow/authoring-and-scheduling/cron.rst

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Cron & Time Intervals
======================
You may set your DAG to run on a simple schedule by setting its ``schedule`` argument to either a
`cron expression <https://en.wikipedia.org/wiki/Cron#CRON_expression>`_, a ``datetime.timedelta`` object,
or one of the :ref:`cron-presets`.

.. code-block:: python

    from airflow.models.dag import DAG

    import datetime

    dag = DAG("regular_interval_cron_example", schedule="0 0 * * *", ...)

    dag = DAG("regular_interval_cron_preset_example", schedule="@daily", ...)

    dag = DAG("regular_interval_timedelta_example", schedule=datetime.timedelta(days=1), ...)
.. _cron-presets:

Cron Presets
''''''''''''
For more elaborate scheduling requirements, you can implement a :doc:`custom timetable <../authoring-and-scheduling/timetable>`.
Note that Airflow parses cron expressions with the croniter library which supports an extended syntax for cron strings. See their documentation `in github <https://github.com/kiorky/croniter>`_.
For example, you can create a DAG schedule to run at 12AM on the first Monday of the month with their extended cron syntax: ``0 0 * * MON#1``.

.. tip::
    You can use an online editor for CRON expressions such as `Crontab guru <https://crontab.guru/>`_

+----------------+--------------------------------------------------------------------+-----------------+
| preset         | meaning                                                            | cron            |
+================+====================================================================+=================+
| ``None``       | Don't schedule, use for exclusively "externally triggered" DAGs    |                 |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@once``      | Schedule once and only once                                        |                 |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@continuous``| Run as soon as the previous run finishes                           |                 |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@hourly``    | Run once an hour at the end of the hour                            | ``0 * * * *``   |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@daily``     | Run once a day at midnight (24:00)                                 | ``0 0 * * *``   |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@weekly``    | Run once a week at midnight (24:00) on Sunday                      | ``0 0 * * 0``   |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@monthly``   | Run once a month at midnight (24:00) of the first day of the month | ``0 0 1 * *``   |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@quarterly`` | Run once a quarter at midnight (24:00) on the first day            | ``0 0 1 */3 *`` |
+----------------+--------------------------------------------------------------------+-----------------+
| ``@yearly``    | Run once a year at midnight (24:00) of January 1                   | ``0 0 1 1 *``   |
+----------------+--------------------------------------------------------------------+-----------------+

Your DAG will be instantiated for each schedule along with a corresponding
DAG Run entry in the database backend.