Airflow 1.9.0 Externaltasksensor Retry_delay=30 Yields Typeerror: Can't Pickle _thread.rlock Objects

As the titles says; in Airflow 1.9.0 if you use the retry_delay=30 (or any other number) parameter with the ExternalTaskSensor, the DAG will run just fine, until you want to clear

Solution 1:

After looking at this problem again, the documentation clearly states that retry_delay should be a timedelta. So its just lucky that the DAG works if you enter an integer instead of a timedelta for retry_delay.

In models.py, BaseOperator:

:paramretry_delay: delay between retries
   :typeretry_delay: timedelta