为什么我的 Airflow 任务被“外部设置为失败”？

我使用的是 Airflow 2.0.0，我的任务在运行几秒钟或几分钟后偶尔会被“外部”终止。任务通常会成功运行（都是通过以下方式启动的手动任务）airflow tasks test ...以及计划的 DAG 运行），所以我相信这与我的 DAG 代码无关。

当任务失败时，这似乎是任务日志中的关键错误：

{local_task_job.py:170} WARNING - State of this instance has been externally set to failed. Terminating instance.

[2020-12-20 11:26:11,448] {taskinstance.py:826} INFO - Dependencies all met for <TaskInstance: daily_backups.run_backupper 2020-12-19T02:00:00+00:00 [queued]>
[2020-12-20 11:26:11,473] {taskinstance.py:826} INFO - Dependencies all met for <TaskInstance: daily_backups.run_backupper 2020-12-19T02:00:00+00:00 [queued]>
[2020-12-20 11:26:11,473] {taskinstance.py:1017} INFO - 
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[2020-12-20 11:26:11,473] {taskinstance.py:1018} INFO - Starting attempt 3 of 3
[2020-12-20 11:26:11,473] {taskinstance.py:1019} INFO - 
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[2020-12-20 11:26:11,506] {taskinstance.py:1038} INFO - Executing <Task(PythonOperator): run_backupper> on 2020-12-19T02:00:00+00:00
[2020-12-20 11:26:11,509] {standard_task_runner.py:51} INFO - Started process 12059 to run task
[2020-12-20 11:26:11,515] {standard_task_runner.py:75} INFO - Running: ['airflow', 'tasks', 'run', 'daily_backups', 'run_backupper', '2020-12-19T02:00:00+00:00', '--job-id', '22', '--pool', 'default_pool', '--raw', '--subdir', 'DAGS_FOLDER/backupper/daily_backups.py', '--cfg-path', '/tmp/tmpnfmqtorg']
[2020-12-20 11:26:11,517] {standard_task_runner.py:76} INFO - Job 22: Subtask run_backupper
[2020-12-20 11:26:11,609] {logging_mixin.py:103} INFO - Running <TaskInstance: daily_backups.run_backupper 2020-12-19T02:00:00+00:00 [running]> on host localhost
[2020-12-20 11:26:11,742] {taskinstance.py:1232} INFO - Exporting the following env vars:
AIRFLOW_CTX_DAG_OWNER=<user>
AIRFLOW_CTX_DAG_ID=daily_backups
AIRFLOW_CTX_TASK_ID=run_backupper
AIRFLOW_CTX_EXECUTION_DATE=2020-12-19T02:00:00+00:00
AIRFLOW_CTX_DAG_RUN_ID=scheduled__2020-12-19T02:00:00+00:00
...
... my job's logs, indicating that the job is running healthily ...
...
[2020-12-20 11:26:16,587] {local_task_job.py:170} WARNING - State of this instance has been externally set to failed. Terminating instance.
[2020-12-20 11:26:16,593] {process_utils.py:95} INFO - Sending Signals.SIGTERM to GPID 12059
[2020-12-20 11:27:16,609] {process_utils.py:108} WARNING - process psutil.Process(pid=12059, name='airflow task runner: daily_backups run_backupper 2020-12-19T02:00:00+00:00 22', status='sleeping', started='11:26:11') did not respond to SIGTERM. Trying SIGKILL
[2020-12-20 11:27:16,618] {process_utils.py:61} INFO - Process psutil.Process(pid=12059, name='airflow task runner: daily_backups run_backupper 2020-12-19T02:00:00+00:00 22', status='terminated', exitcode=<Negsignal.SIGKILL: -9>, started='11:26:11') (12059) terminated with exit code Negsignal.SIGKILL
[2020-12-20 11:27:16,618] {local_task_job.py:118} INFO - Task exited with return code Negsignal.SIGKILL

日志中的最后几行不一致。对于先前尝试中失败的同一任务，这是一个不同的版本：

... same stuff as before ...
[2020-12-20 02:01:12,689] {local_task_job.py:170} WARNING - State of this instance has been externally set to failed. Terminating instance.
[2020-12-20 02:01:12,695] {process_utils.py:95} INFO - Sending Signals.SIGTERM to GPID 24442
[2020-12-20 02:02:00,462] {taskinstance.py:1214} ERROR - Received SIGTERM. Terminating subprocesses.
[2020-12-20 02:02:00,498] {process_utils.py:61} INFO - Process psutil.Process(pid=24442, status='terminated', exitcode=0, started='02:00:10') (24442) terminated with exit code 0
[2020-12-20 02:02:00,499] {local_task_job.py:118} INFO - Task exited with return code 0

我怀疑在这种情况下，脚本能够及时响应 SIGTERM，而在前一种情况下，它在长时间运行的查询上被阻止，并且无法干净地终止。

我相信问题在于调度程序运行状况检查阈值设置为小于调度程序心跳间隔。

在我的配置中我设置了scheduler_health_check_threshold到 30 秒并且scheduler_heartbeat_sec至 60 秒。在检查孤立任务（本身由不同参数控制）期间，orphaned_tasks_check_interval），调度程序心跳被确定为早于 30 秒，这是有道理的，因为它每 60 秒才进行一次心跳。因此调度程序被推断为不健康并因此被终止。

在发生故障时，我可以在/var/log/syslog

Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,368] {scheduler_job.py:1751} INFO - Resetting orphaned tasks for active dag runs
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,373] {scheduler_job.py:1764} INFO - Marked 1 SchedulerJob instances as failed
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,381] {scheduler_job.py:1805} INFO - Reset the following 1 orphaned TaskInstances:
Dec 20 11:26:14 localhost bash[11545]: #011<TaskInstance: daily_backups.run_backupper 2020-12-19 02:00:00+00:00 [running]>
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,571] {scheduler_job.py:938} INFO - 1 tasks up for execution:
Dec 20 11:26:14 localhost bash[11545]: #011<TaskInstance: daily_backups.run_backupper 2020-12-19 02:00:00+00:00 [scheduled]>
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,574] {scheduler_job.py:972} INFO - Figuring out tasks to run in Pool(name=default_pool) with 128 open slots and 1 task instances ready to be queued
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,575] {scheduler_job.py:999} INFO - DAG daily_backups has 0/16 running and queued tasks
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,575] {scheduler_job.py:1060} INFO - Setting the following tasks to queued state:
Dec 20 11:26:14 localhost bash[11545]: #011<TaskInstance: daily_backups.run_backupper 2020-12-19 02:00:00+00:00 [scheduled]>
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,578] {scheduler_job.py:1102} INFO - Sending TaskInstanceKey(dag_id='daily_backups', task_id='run_backupper', execution_date=datetime.datetime(2020, 12, 19, 2, 0, tzinfo=Timezone('UTC')), try_number=4) to executor with priority 2 and queue default
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,578] {base_executor.py:79} INFO - Adding to queue: ['airflow', 'tasks', 'run', 'daily_backups', 'run_backupper', '2020-12-19T02:00:00+00:00', '--local', '--pool', 'default_pool', '--subdir', '/storage/airflow/dags/backupper/daily_backups.py']
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,581] {local_executor.py:81} INFO - QueuedLocalWorker running ['airflow', 'tasks', 'run', 'daily_backups', 'run_backupper', '2020-12-19T02:00:00+00:00', '--local', '--pool', 'default_pool', '--subdir', '/storage/airflow/dags/backupper/daily_backups.py']
Dec 20 11:26:14 localhost bash[11545]: [2020-12-20 11:26:14,707] {dagbag.py:440} INFO - Filling up the DagBag from /storage/airflow/dags/backupper/daily_backups.py
Dec 20 11:26:15 localhost bash[11545]: Running <TaskInstance: daily_backups.run_backupper 2020-12-19T02:00:00+00:00 [queued]> on host localhost

并且时间戳与我的任务收到的​​ SIGTERM 非常吻合。我猜想，由于 SchedulerJob 被标记为失败，因此运行我的实际任务的 TaskInstance 被视为孤儿，因此被标记为终止。同时它安排了一次新的尝试（try_number=4).

增加scheduler_health_check_threshold120 秒并重新启动调度程序/网络服务器服务似乎已经解决了我的问题。