The DateTimeSensor is another part of the Airflow API that seemingly makes no sense. Why would I want to wait until a specified time? For sure, there is little usage of configuration looking like this:
from airflow.sensors.date_time_sensor import DateTimeSensor
time_sensor = DateTimeSensor(
task_id='wait_until_new_year',
target_time='2021-01-01T00:00:00',
)
I could imagine only one situation when it is useful. For example, we may have a DAG that will execute only once when we notify the customers that we have just launched a new product. Such mailing will require a few preparation steps, so we can perform those tasks earlier and then wait until the launch date to send the emails.
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However, the DateTimeSensor can be used with templates, and that makes it way more powerful. If I have a DAG that must wait until 10 am to execute some tasks, I can configure the sensor using the execution_date parameter:
time_sensor = DateTimeSensor(
task_id='are_we_there_yet',
target_time='{{ execution_date.replace(hour=10) }}',
)
What is the advantage of this configuration? When I run a backfill for some past date, it will not get stuck at the time sensor (because the date has already passed). If I used TimeDeltaSensor, it would wait the specified number of minutes even during the backfills, which probably makes no sense.