A trigger rule specifies under what conditions a task starts, depending on the state of its upstream tasks. By default all_success, it can also be one_failed, all_done, or none_failed_min_one_success. It enables cleanup or notification tasks that run even after a failure.
Example
nettoyer = BashOperator(task_id='nettoyer', bash_command='rm -rf /tmp/x', trigger_rule='all_done')