[GitHub] [airflow] ephraimbuddy edited a comment on issue #13681: ExternalTaskSensor can never find External Parent Task

[GitBox <gi...@apache.org>]

ephraimbuddy edited a comment on issue #13681:
URL: https://github.com/apache/airflow/issues/13681#issuecomment-760531896


   The schedule_interval need to be the same for both DAGs for it to work.
   ```
   #
   # Licensed to the Apache Software Foundation (ASF) under one
   # or more contributor license agreements.  See the NOTICE file
   # distributed with this work for additional information
   # regarding copyright ownership.  The ASF licenses this file
   # to you under the Apache License, Version 2.0 (the
   # "License"); you may not use this file except in compliance
   # with the License.  You may obtain a copy of the License at
   #
   #   http://www.apache.org/licenses/LICENSE-2.0
   #
   # Unless required by applicable law or agreed to in writing,
   # software distributed under the License is distributed on an
   # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   # KIND, either express or implied.  See the License for the
   # specific language governing permissions and limitations
   # under the License.
   
   """
   Example DAG demonstrating setting up inter-DAG dependencies using ExternalTaskSensor and
   ExternalTaskMarker
   
   In this example, child_task1 in example_external_task_marker_child depends on parent_task in
   example_external_task_marker_parent. When parent_task is cleared with "Recursive" selected,
   the presence of ExternalTaskMarker tells Airflow to clear child_task1 and its
   downstream tasks.
   
   ExternalTaskSensor will keep poking for the status of remote ExternalTaskMarker task at a regular
   interval till one of the following will happen:
   1. ExternalTaskMarker reaches the states mentioned in the allowed_states list
       In this case, ExternalTaskSensor will exit with a succes status code
   2. ExternalTaskMarker reaches the states mentioned in the failed_states list
       In this case, ExternalTaskSensor will raise an AirflowException and user need to handle this
       with multiple downstream tasks
   3. ExternalTaskSensor times out
       In this case, ExternalTaskSensor will raise AirflowSkipException or AirflowSensorTimeout
       exception
   """
   
   import datetime
   
   from airflow import DAG
   from airflow.operators.dummy import DummyOperator
   from airflow.sensors.external_task import ExternalTaskMarker, ExternalTaskSensor
   
   start_date = datetime.datetime(2015, 1, 1)
   
   with DAG(
       dag_id="example_external_task_marker_parent",
       start_date=start_date,
       schedule_interval=datetime.timedelta(minutes=30),
       tags=['example2'],
   ) as parent_dag:
       # [START howto_operator_external_task_marker]
       parent_task = ExternalTaskMarker(
           task_id="parent_task",
           external_dag_id="example_external_task_marker_child",
           external_task_id="child_task1",
       )
       # [END howto_operator_external_task_marker]
   
   with DAG(
       dag_id="example_external_task_marker_child",
       start_date=start_date,
       schedule_interval=datetime.timedelta(minutes=30),
       tags=['example2'],
   ) as child_dag:
       # [START howto_operator_external_task_sensor]
       child_task1 = ExternalTaskSensor(
           task_id="child_task1",
           external_dag_id=parent_dag.dag_id,
           external_task_id=parent_task.task_id,
           timeout=600,
           allowed_states=['success'],
           failed_states=['failed', 'skipped'],
           mode="reschedule",
       )
       # [END howto_operator_external_task_sensor]
       child_task2 = DummyOperator(task_id="child_task2")
       child_task1 >> child_task2
   ```


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