I was trying to schedule an airflow dag that given a start date it will trigger that dag after every scheduled interval. This is what my dag definition looks like.
with DAG('Some Dag',
start_date=datetime(year=2020, month=12, day=23),
schedule_interval=timedelta(days=1, hours=5, minutes=0),
catchup=False) as dag:
Doesn't it mean that the DAG will run on 2020/12/24 at 05:00:00 UTC? But in reality, it isn't triggering at that moment.
I know I can easily achieve this via a Cron expression. But I want to do it without a Cron expression.
Related
I am completely new to Airflow and am trying to grasp the concepts of scheduling and default args.
I have a scenario where I would like to schedule my DAG hourly to do some data transfer task between a source and a database. What I am trying to understand is, lets say one of my DAG runs has triggered at 00:00 AM. Now if it takes more than an hour for this run to successfully complete all of its tasks (say 1 hour 30 min), does it mean that the next DAG run that was supposed to be triggered at 01:00 AM will NOT get triggered but the DAG run from 02:00 AM will get triggered?
Yes.
In order to avoid, you need catchup=True for the DAG object.
Reference : https://airflow.apache.org/docs/apache-airflow/stable/dag-run.html
(Search for Catchup)
Airflow Scheduler used to monitor all DAGs and tasks in Airflow.Default Arguments can be used to create tasks with default parameters in DAG.
The first DAG runs based on start_date and runs based on scheduled_interval sequentially. Scheduler doesn’t trigger tasks until the period has ended.For your requirement you can set dag.catchup to true as to run the DAG for each completed interval and scheduler will execute them sequentially.Catchup is used to start the DAG run since the last data interval which has not started for any data interval.
I am trying to define periods of time where the scheduler will not mark tasks as ready.
For example, I have a DAG with a lengthy backfill period. The execution of the backfill will run throughout the day until the DAG is caught up. However I do not want and executions of the DAG to execute between midnight and 2 am.
Is it possible to achieve this through configuration?
I want to set up a dag there are few cases that I would like to address while creating the dag.
Next run of the dag should be skiped if the current dag is in execution or failed, using catchup=False and max_active_runs=1 for this, do I need to use wait_for_downstream for this?
Should it be skipped or not scheduled to run.... an argument of depends_on_past: True in your DAG args might be what you need depending on your requirements.
I have multiple dags that run on different cadence: some weekly, some daily etc. I want it to setup such that while dag-a is running, dag-b should wait until it is completed. Also, if dag-b is running dag-a should wait until dag-b completes, etc. Is there a way to do this in airflow out of the box?
What you are looking for is probably the ExternalTaskSensor
Airflow's Cross-DAG Dependencies description is also pretty useful.
If you are using this, there is also the Airflow DAG dependencies plugin, which can be pretty useful for visualizating those dependencies.
You could use the sensor operator to sense the dag runs or a task in a dag run. External task sensor is the best bet. Be careful how you set the timedelta passed. In general, the idea is to specify the when should the sensor be able to find the dag run.
Eg:
If the main dag is scheduled at 4 UTC, and a task sensor is a task in the dag like below
ExternalTaskSensor(
dag=dag,
task_id='dag_sensor_{}'.format(key),
external_dag_id=key,
timedelta=timedelta(days=1),
external_task_id=None,
mode='reschedule',
check_existence=True
)
Then the other dag that should get sensed must be triggering a run at 4.00UTC. That one day difference is set to offset the difference of execution date and current date
I have a dag that is scheduled to call a script daily passing the current date so i pass {{ ds }} to get the execution date.
On days when my dag doesn't run i have catchup = True.
so the dag needs to pass the scheduled date, not the execution date for the task to get done, so that the activity of the day on which the dag was unable to run is still completed.
How can i do this?
As far as I understand your scenario, the execution_date is exactly what you need.
The name might be a bit misleading, but it is in fact filled with the scheduled timestamp.