如何使用 Python 在 Airflow 中的另一个 DAG 成功时触发 DAG？

Question

我有一个 python DAG Parent Job 和一个 DAG Child Job。 Child Job 中的任务应在成功完成每天运行的 Parent Job 任务时触发。如何添加外部作业触发器？

我的代码

from datetime import datetime, timedelta
from airflow import DAG
from airflow.operators.postgres_operator import PostgresOperator
from utils import FAILURE_EMAILS

yesterday = datetime.combine(datetime.today() - timedelta(1), datetime.min.time())


default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': yesterday,
    'email': FAILURE_EMAILS,
    'email_on_failure': False,
    'email_on_retry': False,
    'retries': 1,
    'retry_delay': timedelta(minutes=5)
}

dag = DAG('Child Job', default_args=default_args, schedule_interval='@daily')

execute_notebook = PostgresOperator(
  task_id='data_sql',
  postgres_conn_id='REDSHIFT_CONN',
  sql="SELECT * FROM athena_rs.shipments limit 5",
  dag=dag
)

Answer 1

我相信您正在寻找 SubDags operator、运行一个更大的 Dag。请注意，像下面的示例一样创建许多子标签很快就会变得混乱，因此我建议将每个子标签拆分到一个文件中，然后导入到一个主文件中。

SubDagOperator 简单易用你需要给一个 Id，一个 subdag（子）和一个 dag（父）

subdag_2 = SubDagOperator(
        task_id="just_some_id", 
        subdag=child_subdag, <---- this must be a DAG
        dag=parent_dag, <----- this must be a DAG
        )

它看起来像这样：

来自 their examples repo

from airflow import DAG
from airflow.example_dags.subdags.subdag import subdag
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.subdag_operator import SubDagOperator
from airflow.utils.dates import days_ago
from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator
def subdag(parent_dag_name, child_dag_name, args):
    dag_subdag = DAG(
            dag_id='%s.%s' % (parent_dag_name, child_dag_name),
            default_args=args,
            schedule_interval="@daily",
            )

    for i in range(5):
        DummyOperator(
                task_id='%s-task-%s' % (child_dag_name, i + 1),
                default_args=args,
                dag=dag_subdag,
                )

    return dag_subdag

DAG_NAME = 'example_subdag_operator'

args = {
        'owner': 'airflow',
        'start_date': days_ago(2),
        }

dag = DAG(
        dag_id=DAG_NAME,
        default_args=args,
        schedule_interval="@once",
        tags=['example']
        )

start = DummyOperator(
        task_id='start-of-main-job',
        dag=dag,
        )

some_other_task = DummyOperator(
        task_id='some-other-task',
        dag=dag,
        )


end = DummyOperator(
        task_id='end-of-main-job',
        dag=dag,
        )

subdag = SubDagOperator(
        task_id='run-this-dag-after-previous-steps',
        subdag=subdag(DAG_NAME, 'run-this-dag-after-previous-steps', args),
        dag=dag,
        )

start >> some_other_task >> end >> subdag

Answer 2

答案已经在中。下面是演示代码：

Parent 天:

from datetime import datetime
from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator

default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': datetime(2020, 4, 29),
}

dag = DAG('Parent_dag', default_args=default_args, schedule_interval='@daily')

leave_work = DummyOperator(
    task_id='leave_work',
    dag=dag,
)
cook_dinner = DummyOperator(
    task_id='cook_dinner',
    dag=dag,
)

leave_work >> cook_dinner

Child 天:

from datetime import datetime, timedelta
from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.sensors import ExternalTaskSensor

default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': datetime(2020, 4, 29),
}

dag = DAG('Child_dag', default_args=default_args, schedule_interval='@daily')

# Use ExternalTaskSensor to listen to the Parent_dag and cook_dinner task
# when cook_dinner is finished, Child_dag will be triggered
wait_for_dinner = ExternalTaskSensor(
    task_id='wait_for_dinner',
    external_dag_id='Parent_dag',
    external_task_id='cook_dinner',
    start_date=datetime(2020, 4, 29),
    execution_delta=timedelta(hours=1),
    timeout=3600,
)

have_dinner = DummyOperator(
    task_id='have_dinner',
    dag=dag,
)
play_with_food = DummyOperator(
    task_id='play_with_food',
    dag=dag,
)

wait_for_dinner >> have_dinner
wait_for_dinner >> play_with_food

图片：

狗

Parent_dag

Child_dag

Answer 3

作为 by @pankaj，我特此添加一段描述 反应式触发 使用 TriggerDagRunOperator（相对于 poll-基于触发 of ExternalTaskSensor)

from typing import List

from airflow.models.baseoperator import BaseOperator
from airflow.models.dag import DAG
from airflow.operators.dagrun_operator import TriggerDagRunOperator
from airflow.utils.trigger_rule import TriggerRule

# DAG object
my_dag: DAG = DAG(dag_id='my_dag',
                  start_date=..)
..
# a list of 'tail' tasks: tasks that have no downstream tasks
tail_tasks_of_first_dag: List[BaseOperator] = my_magic_function_that_determines_all_tail_tasks(..)
..

# our trigger task
my_trigger_task: TriggerDagRunOperator = TriggerDagRunOperator(dag=my_dag,
                                                               task_id='my_trigger_task',
                                                               trigger_rule=TriggerRule.ALL_SUCCESS,
                                                               external_dag_id='id_of_dag_to_be_triggered')
# our trigger task should run when all 'tail' tasks have completed / succeeded
tail_tasks_of_first_dag >> my_trigger_task

请注意，该片段仅供参考；尚未经过测试

注意事项/参考资料

Get all Airflow Leaf Nodes/Tasks

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