I recently openend the following PR: https://github.com/apache/incubator-airflow/pull/2877
The problem is that on_kill is not called for operators when you clear a task from the UI. Thats problematic when working with ex. spark clusters as the jobs on the cluster need to be killed. The issue is in the core code of Airflow and Im not familiar enough with the inner workings there. So I could use some directions on this one from people who are familiar. For more info, check out the PR. Kind regards, Milan
