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https://issues.apache.org/jira/browse/AIRFLOW-151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15292631#comment-15292631
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Siddharth Anand edited comment on AIRFLOW-151 at 5/20/16 4:39 AM:
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Answer ported from the external issue.
was (Author: sanand):
Answer duplicated from the external issue.
> trigger_rule='one_success' not allowing tasks downstream of a
> BranchPythonOperator to be executed
> -------------------------------------------------------------------------------------------------
>
> Key: AIRFLOW-151
> URL: https://issues.apache.org/jira/browse/AIRFLOW-151
> Project: Apache Airflow
> Issue Type: Bug
> Reporter: Siddharth Anand
> Assignee: Siddharth Anand
> Attachments: DAG_Problem.png
>
>
> Porting from https://github.com/apache/incubator-airflow/issues/1521
> Dear Airflow Maintainers,
> *Environment*
> {panel}
> Airflow version: 1.7.0rc3
> Airflow components: webserver, scheduler, worker, postgres database,
> CeleryExecutor
> Relevant airflow.cfg settings: nothing special here; mostly defaults
> Python Version: 3.4.3
> Operating System: Centos 6.7
> Python packages: virtualenv with standard airflow install
> {panel}
> *Background*
> We are constructing a workflow to automate standard business processes around
> the creation and maintenance of virtual machines. After creation, we verify
> several information points on the VM to ensure that it is a viable machine
> and that no configuration errors occurred. If it fails verification and is
> not running, then it should be deleted. If it fails verification and is
> running, then we stop it first, then delete it.
> *What did you expect to happen?*
> After researching the BranchPythonOperator, I found that I should be using
> trigger_rule='one_success' to allow a task at a join point downstream of the
> branch(es) to be triggered, as mentioned in #1078. So, I defined the task as
> follows:
> {code}
> delete_vm = PythonOperator(
> task_id='delete_vm',
> trigger_rule=TriggerRule.ONE_SUCCESS,
> python_callable=_delete_vm,
> provide_context=True,
> dag=dag)
> delete_vm.set_upstream({poll_vm_stop, verify_vm})
> {code}
> *What happened instead?*
> Rather than executing correctly, the delete_vm task is marked as skipped and
> is not re-evaluated following poll_vm_stop. There is no stack trace
> available, as the task simply does not execute. Sidenote: the PythonSensor
> you see in the picture below is a sensor which evaluates the truthy- or
> falsey-ness of a Python callable. It has been tested extensively and works as
> intended.
> !DAG_Problem.png!
> Any help would be greatly appreciated. I've tested various ways of linking
> the dag, providing DummyOperators as buffers, using a second
> BranchPythonOperator to explicitly call the task; all of these have failed.
> Am I missing something obvious here?
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