[jira] [Commented] (AIRFLOW-564) DagRunOperator and ExternalTaskSensor Incompatibility

["Laura Lorenz (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15565570#comment-15565570 ] 

Laura Lorenz commented on AIRFLOW-564:
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For us this hasn't leaked into the problem as described here, but we do have an execution_date aware DAG that is triggered via another DAG's TriggerDagRunOperator, and we have to send the parent DAG's execution_date as part of the payload to its child. I can see how it could escalate into the problem [~martingrayson] describes if we threw an ExternalTaskSensor into the mix. I think it makes a lot more intuitive sense for the child DAG's DagRun to inherit the execution_date of its parent DAG, not one that is mirrored by the DagRun's start_date.

> DagRunOperator and ExternalTaskSensor Incompatibility
> -----------------------------------------------------
>
>                 Key: AIRFLOW-564
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-564
>             Project: Apache Airflow
>          Issue Type: Task
>          Components: DagRun
>    Affects Versions: Airflow 1.7.1.3
>            Reporter: Martin Grayson
>         Attachments: 1.controller.png, 2. par.png, 3. dep.png, dep_dag.py, parent_dag.py, test_dag_scheduler.py
>
>
> I have an hourly Dag that acts to orchestrate other dags, triggering dag runs if a precondition is met.
> The controller dag (Dag CD) uses a `TriggerDagRunOperator` operator to do this, launching 2 other dags (Dag A, Dag B) in my example (10+ in my real life). 
> Within these dags they have their own dependencies, for example Dag B is dependent on Dag A's completion. This is handled using a `ExternalTaskSensor`. 
> Since Dag A and B are executed dynamically with the `TriggerDagRunOperator`, they're assigned very granular execution dates, rather than dd-mm-yyyy hh:00:00 as the scheduler would assign.  Due to this, the `ExternalTaskSensor` will not succeed unless Dag A and B managed to have exactly the same execution_date (down to the second).
> As far as I can tell, I'm not able to force the `ExternalTaskSensor` to poke for the correct execution date. The only possible solution would be to implement a `execution_date_fn` that looked through the metadata db to find the exact execution time. This seems massively complicated for a relatively simple requirement.
> Can this scenario be modelled with these components?
> I've attached a set of example dags and some screenshots, showing the issue.
> Thanks,
> Martin



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