Got it,   

But here you are just stopping the NB execution right, but i want the for loop iteration to get stooped for that rootrunid. Let's say i have a for each loop in workflow inside which i have a job, for each iteration to be stooped/failed if one of the iteration fails.

if existing_failure > 0:
dbutils.notebook.exit("Exiting due to a previously logged failure.").

i tried something like this to cancel the job based on run id for that loop job but its cancelling , i need to make it fail,not cancel: