What start_date should I use for a manually triggered DAG?

Question

Many of the airflow example dags that have schedule_interval=None set a dynamic start date like airflow.utils.dates.days_ago(2) or datetime.utcnow(). However, the docs recommend against a dynamic start date:

We recommend against using dynamic values as start_date, especially datetime.now() as it can be quite confusing. The task is triggered once the period closes, and in theory an @hourly DAG would never get to an hour after now as now() moves along.

Is start date irrelevant for manually triggered dags? What is the best practice here?

Answer 1

If you have a schedule_interval=None I believe the start_date is irrelevant as airflow will not attempt to perform any back filling. Just set it to anything even if it's a dynamic one it shouldn't cause any hassle.

Answer 2

I ended up just setting start_date to 1970, Jan 1st (absurdly far in the past) so that Airflow never complains that the execution date is before the start date.