气流:当上游被短路跳过时运行任务 [英] Airflow : Run a task when some upstream is skipped by shortcircuit

问题描述

我有一个名为"c0"的任务，该任务具有多个上游连接.当上游之一被ShortCircuitOperator跳过时，该任务也将被跳过.我不想跳过final任务，因为它必须报告DAG成功.

I have a task that I'll call final that has multiple upstream connections. When one of the upstreams gets skipped by ShortCircuitOperator this task gets skipped as well. I don't want final task to get skipped as it has to report on DAG success.

为避免被跳过，我使用了trigger_rule='all_done'，但仍然被跳过了.

To avoid it getting skipped I used trigger_rule='all_done', but it still gets skipped.

如果我使用BranchPythonOperator而不是ShortCircuitOperator final，则不会跳过任务.即使不是最佳选择，分支工作流似乎也是一个解决方案，但是现在final将不再考虑上游任务的失败.

If I use BranchPythonOperator instead of ShortCircuitOperator final task doesn't get skipped. It would seem like branching workflow could be a solution, even though not optimal, but now final will not respect failures of upstream tasks.

如何使它仅在成功运行或跳过上游时运行?

How do I get it to only run when upstreams are successful or skipped?

示例短路DAG:

from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.python_operator import ShortCircuitOperator
from datetime import datetime
from random import randint

default_args = {
    'owner': 'airflow',
    'start_date': datetime(2018, 8, 1)}

dag = DAG(
    'shortcircuit_test',
    default_args=default_args,
    schedule_interval='* * * * *',
    catchup=False)

def shortcircuit_fn():
    return randint(0, 1) == 1

task_1 = DummyOperator(dag=dag, task_id='task_1')
task_2 = DummyOperator(dag=dag, task_id='task_2')

work = DummyOperator(dag=dag, task_id='work')
short = ShortCircuitOperator(dag=dag, task_id='short_circuit', python_callable=shortcircuit_fn)
final = DummyOperator(dag=dag, task_id="final", trigger_rule="all_done")

task_1 >> short >> work >> final
task_1 >> task_2 >> final

示例分支DAG:

from airflow import DAG
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.python_operator import BranchPythonOperator
from datetime import datetime
from random import randint

default_args = {
    'owner': 'airflow',
    'start_date': datetime(2018, 8, 1)}

dag = DAG(
    'branch_test',
    default_args=default_args,
    schedule_interval='* * * * *',
    catchup=False)

# these two are only here to protect tasks from getting skipped as direct dependencies of branch operator
to_do_work = DummyOperator(dag=dag, task_id='to_do_work')
to_skip_work = DummyOperator(dag=dag, task_id='to_skip_work')

def branch_fn():
    return to_do_work.task_id if randint(0, 1) == 1 else to_skip_work.task_id

task_1 = DummyOperator(dag=dag, task_id='task_1')
task_2 = DummyOperator(dag=dag, task_id='task_2')

work = DummyOperator(dag=dag, task_id='work')
branch = BranchPythonOperator(dag=dag, task_id='branch', python_callable=branch_fn)
final = DummyOperator(dag=dag, task_id="final", trigger_rule="all_done")

task_1 >> branch >> to_do_work >> work >> final
branch >> to_skip_work >> final
task_1 >> task_2 >> final

推荐答案

我最终基于原始模型开发了定制的ShortCircuitOperator:

I've ended up with developing custom ShortCircuitOperator based on the original one:

class ShortCircuitOperator(PythonOperator, SkipMixin):
    """
    Allows a workflow to continue only if a condition is met. Otherwise, the
    workflow "short-circuits" and downstream tasks that only rely on this operator
    are skipped.

    The ShortCircuitOperator is derived from the PythonOperator. It evaluates a
    condition and short-circuits the workflow if the condition is False. Any
    downstream tasks that only rely on this operator are marked with a state of "skipped".
    If the condition is True, downstream tasks proceed as normal.

    The condition is determined by the result of `python_callable`.
    """

    def find_tasks_to_skip(self, task, found_tasks=None):
        if not found_tasks:
            found_tasks = []
        direct_relatives = task.get_direct_relatives(upstream=False)
        for t in direct_relatives:
            if len(t.upstream_task_ids) == 1:
                found_tasks.append(t)
                self.find_tasks_to_skip(t, found_tasks)
        return found_tasks

    def execute(self, context):
        condition = super(ShortCircuitOperator, self).execute(context)
        self.log.info("Condition result is %s", condition)

        if condition:
            self.log.info('Proceeding with downstream tasks...')
            return

        self.log.info(
            'Skipping downstream tasks that only rely on this path...')

        tasks_to_skip = self.find_tasks_to_skip(context['task'])
        self.log.debug("Tasks to skip: %s", tasks_to_skip)

        if tasks_to_skip:
            self.skip(context['dag_run'], context['ti'].execution_date,
                      tasks_to_skip)

        self.log.info("Done.")

此操作员确保不会因一个跳过的任务而跳过依赖多个路径的下游任务.

This operator makes sure no downstream task that rely on multiple paths are getting skipped because of one skipped task.

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