eladkal edited a comment on issue #17585:
URL: https://github.com/apache/airflow/issues/17585#issuecomment-902014936
> Add another task with depends_on_past=True to the existing DAG
I think the issue here is that you assume that when you add a new task
Airflow knows that it starts from the date you added it thus you expect
`depends_on_past=True` to work but this is not the case. You must provide a
`start_date` to this new task for the `depends_on_past` to work.
```
from airflow import DAG
from airflow.operators.dummy import DummyOperator
from datetime import datetime
default_args = {
'owner': 'Elad',
'start_date': datetime(2021, 8, 19),
}
with DAG('my_dag2', default_args=default_args, schedule_interval='*/5 * * *
*') as dag:
a = DummyOperator(task_id="1st")
b = DummyOperator(task_id="2nd", wait_for_downstream=True)
a >> b
with DAG('my_dag3', default_args=default_args, schedule_interval='*/5 * * *
*') as dag:
a = DummyOperator(task_id="1st")
b = DummyOperator(task_id="2nd", wait_for_downstream=True,
start_date=datetime(2021, 8, 19, 15, 15))
a >> b
```
as you can see `my_dag3` works fine yet `my_dag2` is stuck:
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