Default 'once' start_date to 'now' when None #50760
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eladkal
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May 19, 2025
eladkal
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May 19, 2025
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Previously, when a dag does not have start_date, 'once' would never run because the scheduler does not know when to do that one run. This was not particularly problematic in Airflow 2 since you almost always are expected to provide an explicit start_date to a dag. In Airflow 3, however, since start_date=None is the implicit default, it is more common for people to forget about the start_date, and be surprised when the dag never runs. After some brief discussion, it's decided that it's more intuitive for this argument combination to run the dag 'as soon as convenient' instead. See also: https://apache-airflow.slack.com/archives/C06K9Q5G2UA/p1747371756970659
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Lee-W
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Previously, when a dag does not have start_date, 'once' would never run because the scheduler does not know when to do that one run. This was not particularly problematic in Airflow 2 since you almost always are expected to provide an explicit start_date to a dag.
In Airflow 3, however, since start_date=None is the implicit default, it is more common for people to forget about the start_date, and be surprised when the dag never runs. After some brief discussion, it's decided that it's more intuitive for this argument combination to run the dag 'as soon as convenient' instead.
See also: https://apache-airflow.slack.com/archives/C06K9Q5G2UA/p1747371756970659
Close #50374.