title: Airflow - Why is there no trigger rule "One done"? Am i missing something?
body: <p>I am trying to do this flow in an airflow dag.</p>
  
  <ul>
  <li>Task 1: check if file exists in s3 (s3 sensor). If no new file is found, skip to task 4.</li>
  <li>Task 2: if task 1 meets the criteria, delete the existing file in the local folder</li>
  <li>Task 3: if task 2 is finished, download the s3 file into the local folder</li>
  <li>Task 4: in either case, update table (using the only file in the folder)</li>
  </ul>
  
  <p>I am not sure what trigger rule to add in the task 4. If i add one_failed, obviously the task wont be executed if the file exists.</p>
  
  <p>If i add "all_done" it wont be executed because in either path, the dag will be skipping tasks (that's the whole purpose).</p>
  
  <p>How should I go about it? I think i am missing something here...</p>
  
  <p>Thanks everyone.</p>
  
  <p><em>UPDATE</em></p>
  
  <p>It also seems that my s3keysensor is not triggering "Fail" status when timed out. It appears in yellow even though the log shows "Snap, time is out".</p>
  
  <p>Should be triggering Fail. This is from the documentation.
  "    Sensor operators keep executing at a time interval and succeed when
          a criteria is met and fail if and when they time out."</p>
  
  <p>This message appears in the console "These tasks are deadlocked: {...}." and the dag does not keep running. Can't get task 4 running! I am also trying it with a backfill for the same start and end date, is this correct?</p>