title: Airflow task running succesful but showing SIGTERM error
body: <p>I have one airflow task which log shows that ran succesfull, but same log also show SIGTERM.</p>
  <pre><code>[2021-11-30 00:52:25,481] {taskinstance.py:1087} INFO - 
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  [2021-11-30 00:52:25,481] {taskinstance.py:1088} INFO - Starting attempt 1 of 11
  [2021-11-30 00:52:25,482] {taskinstance.py:1089} INFO - 
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  [2021-11-30 00:52:25,492] {taskinstance.py:1107} INFO - Executing &lt;Task(PythonOperator): &gt; on 2021-11-29T00:30:00+00:00
  [2021-11-30 00:52:25,500] {standard_task_runner.py:52} INFO - Started process 11633 to run task
  
  [2021-11-30 00:52:25,509] {standard_task_runner.py:77} INFO - Job 1580251: Subtask 
  [2021-11-30 00:52:25,609] {logging_mixin.py:104} INFO - Running &lt;TaskInstance: DWH_D_V1.1.0.transform 2021-11-29T00:30:00+00:00 [running]&gt; on host 
  [2021-11-30 00:52:25,718] {taskinstance.py:1300} INFO - Exporting the following env vars:
  
  AIRFLOW_CTX_EXECUTION_DATE=2021-11-29T00:30:00+00:00
  AIRFLOW_CTX_DAG_RUN_ID=scheduled__2021-11-29T00:30:00+00:00
  [2021-11-30 00:52:26,105] {transform.py:55} INFO - Empty 
  [2021-11-30 00:52:26,755] {transform.py:58} INFO - Inserting values
  [2021-11-30 01:07:54,098] {db_table.py:561} INFO - Datadog metrics push
  [2021-11-30 01:07:54,099] {hostname.py:60} INFO - No agent or invalid configuration file found
  [2021-11-30 01:07:54,113] {db_table.py:573} INFO - Datadog push: Number of rows: 47951835 
  [2021-11-30 01:07:54,405] {api_client.py:138} INFO - 202 POST 
  [2021-11-30 01:07:54,405] {datadog_logger.py:65} INFO - Datadog push: {'status': 'ok'}
  [2021-11-30 01:07:54,405] {db_table.py:586} INFO - Datadog push: Execution time: 928.146014213562 s
  [2021-11-30 01:07:54,477] {api_client.py:138} INFO - 202 POST https://api.datadoghq.com/api/v1/series (71.0046ms)
  [2021-11-30 01:07:54,477] {datadog_logger.py:65} INFO - Datadog push: {'status': 'ok'}
  [2021-11-30 01:07:54,477] {transform_dim_simple.py:66} INFO - Done
  [2021-11-30 01:07:54,478] {python.py:151} INFO - Done. Returned value was: None
  [2021-11-30 01:07:54,501] {taskinstance.py:1204} INFO - Marking task as SUCCESS. dag_id=DWH_D_V1.1.0, task_id=trasnform, execution_date=20211129T003000, start_date=20211130T005225, end_date=20211130T010754
  [2021-11-30 01:07:54,705] {local_task_job.py:197} WARNING - State of this instance has been externally set to success. Terminating instance.
  [2021-11-30 01:07:54,707] {process_utils.py:100} INFO - Sending Signals.SIGTERM to GPID 11633
  [2021-11-30 01:07:54,753] {taskinstance.py:1284} ERROR - Received SIGTERM. Terminating subprocesses.
  [2021-11-30 01:07:54,753] {logging_mixin.py:104} WARNING - Exception ignored in: &lt;function _collection_gced at 0x7f4e1ca08f70&gt;
  [2021-11-30 01:07:54,753] {logging_mixin.py:104} WARNING - Traceback (most recent call last):
  [2021-11-30 01:07:54,753] {logging_mixin.py:104} WARNING -   File &quot;/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/event/registry.py&quot;, line 53, in _collection_gced
  [2021-11-30 01:07:54,754] {logging_mixin.py:104} WARNING -     def _collection_gced(ref):
  [2021-11-30 01:07:54,754] {logging_mixin.py:104} WARNING -   File &quot;/home/airflow/.local/lib/python3.8/site-packages/airflow/models/taskinstance.py&quot;, line 1286, in signal_handler
  [2021-11-30 01:07:54,755] {logging_mixin.py:104} WARNING -     raise AirflowException(&quot;Task received SIGTERM signal&quot;)
  [2021-11-30 01:07:54,755] {logging_mixin.py:104} WARNING - airflow.exceptions.AirflowException: Task received SIGTERM signal
  [2021-11-30 01:07:54,802] {taskinstance.py:1265} INFO - 1 downstream tasks scheduled from follow-on schedule check
  [2021-11-30 01:07:54,840] {process_utils.py:66} INFO - Process psutil.Process(pid=11633, status='terminated', exitcode=0, started='00:52:25') (11633) terminated with exit code 0
  </code></pre>
  <p>I know task has been succesfull because datadog shows a metric push on that day for that process. After that airflow receives an external trigger or something like that, but I am sure that nobody mark the task as succeed manually and we dont have any process that changes the state of that process.</p>
  <p>This only happened twice randomly.</p>
  <p>Is this a known behavior or there is any kind of hint to investigate. I though on increasing <code>AIRFLOW_CORE_KILLED_TASK_CLEANUP_TIME</code> but as it is random and it happened few times didn't know even how to check if it was the solution in case it work fine.</p>