Trigger rules (all_success, one_success, none_failed) in Apache Airflow - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the trigger rule all_success mean in Airflow?

The all_success trigger rule means the task will run only if all of its upstream tasks have completed successfully.

beginner

Explain the one_success trigger rule in Airflow.

The one_success trigger rule means the task will run if at least one of its upstream tasks has succeeded, regardless of others' states.

intermediate

What does the none_failed trigger rule ensure before running a task?

The none_failed trigger rule ensures the task runs only if none of its upstream tasks have failed. It allows upstream tasks to be skipped but not failed.

intermediate

If a task has three upstream tasks: two succeeded and one failed, which trigger rule will allow the task to run?

Only the one_success trigger rule will allow the task to run because at least one upstream task succeeded. all_success and none_failed will not run the task.

intermediate

Why might you use none_failed instead of all_success?

Use none_failed when you want the task to run as long as no upstream task failed, even if some were skipped. This is useful when skips are acceptable but failures are not.

Which trigger rule runs a task only if all upstream tasks succeeded?

A all_done

B one_success

C none_failed

D all_success

The all_success trigger rule requires every upstream task to succeed before running.

If one upstream task succeeded and others failed, which trigger rule allows the task to run?

A one_success

B all_success

C none_failed

D dummy

one_success runs the task if at least one upstream task succeeded.

Which trigger rule allows running if no upstream task failed, even if some were skipped?

A one_success

B none_failed

C all_success

D all_failed

none_failed allows running if no upstream tasks failed, skips are allowed.

What happens if a task uses all_success but one upstream task is skipped?

A Task does not run

B Task skips

C Task runs

D Task fails

all_success requires all upstream tasks to succeed; skipped upstream tasks prevent running.

Which trigger rule is best when you want to run a task if any upstream task succeeded?

A none_failed

B all_success

C one_success

D all_done

one_success runs the task if at least one upstream task succeeded.

Describe the differences between the trigger rules all_success, one_success, and none_failed in Airflow.

Think about how many upstream tasks must succeed or fail for each rule.

Give an example scenario where using none_failed is better than all_success.

Consider situations where skipping is acceptable but failure is not.

Practice

1. In Airflow, which trigger rule ensures a task runs only if all upstream tasks have succeeded?

easy

A. all_success

B. one_success

C. none_failed

D. all_failed

Solution

1. Step 1: Understand the meaning of all_success

   This trigger rule requires every upstream task to complete successfully before the downstream task runs.

2. Step 2: Compare with other trigger rules

   one_success runs if any upstream succeeds, none_failed runs if no upstream failed (some may be skipped), and all_failed runs only if all upstream failed.

3. Final Answer:

   all_success -> Option A

4. Quick Check:

   All upstream success = all_success [OK]

Hint: All upstream must succeed means all_success [OK]

Common Mistakes:

• Confusing one_success with all_success
• Thinking none_failed means all succeeded
• Assuming all_failed runs on success

2. Which of the following is the correct way to set a task's trigger rule to run if at least one upstream task succeeds in Airflow DAG code?

easy

A. trigger_rule='all_success'

B. trigger_rule='all_done'

C. trigger_rule='none_failed'

D. trigger_rule='one_success'

Solution

1. Step 1: Recall the trigger rule for running on any upstream success

   The trigger rule one_success runs the task if at least one upstream task succeeded.

2. Step 2: Check syntax correctness

   Setting trigger_rule='one_success' is the correct syntax in Airflow task definition.

3. Final Answer:

   trigger_rule='one_success' -> Option D

4. Quick Check:

   At least one success = trigger_rule='one_success' [OK]

Hint: Use trigger_rule='one_success' for any upstream success [OK]

Common Mistakes:

• Using all_success instead of one_success
• Misspelling trigger_rule or using wrong quotes
• Confusing none_failed with one_success

3. Given a DAG with three upstream tasks: task1 (success), task2 (skipped), task3 (failed). If a downstream task uses trigger_rule='none_failed', will it run?

medium

A. Yes, because no upstream task failed

B. No, because one upstream task failed

C. Yes, because at least one upstream succeeded

D. No, because all upstream tasks must succeed

Solution

1. Step 1: Understand none_failed trigger rule

   This rule runs the task only if no upstream task has failed. If any upstream failed, it will not run.

2. Step 2: Analyze upstream task states

   task3 failed, so the condition of no failures is false. Therefore, the downstream task will not run.

3. Final Answer:

   No, because one upstream task failed -> Option B

4. Quick Check:

   Any failure blocks none_failed run [OK]

Hint: If any upstream failed, none_failed won't run [OK]

Common Mistakes:

• Ignoring failed upstream tasks when using none_failed
• Confusing skipped with failed states
• Assuming none_failed runs if some succeed

4. You have a task with trigger_rule='one_success' but it never runs even though some upstream tasks succeed. What is the likely cause?

medium

A. The task has no upstream dependencies defined

B. The DAG is paused

C. The trigger_rule is misspelled or not set correctly

D. All upstream tasks failed

Solution

1. Step 1: Check trigger_rule spelling and assignment

   If the trigger_rule is misspelled or not properly set, Airflow defaults to all_success, causing the task not to run if not all upstream succeed.

2. Step 2: Verify other conditions

   Since some upstream succeed, and the task has dependencies, the most common cause is incorrect trigger_rule syntax.

3. Final Answer:

   The trigger_rule is misspelled or not set correctly -> Option C

4. Quick Check:

   Incorrect trigger_rule causes unexpected task skipping [OK]

Hint: Check trigger_rule spelling if task doesn't run as expected [OK]

Common Mistakes:

• Assuming upstream failure when some succeeded
• Ignoring DAG paused state
• Not defining upstream dependencies

5. You want a downstream task to run if either all upstream tasks succeed or if none failed but some were skipped. Which trigger rule should you use?

hard

A. none_failed

B. one_success

C. all_success

D. all_done

Solution

1. Step 1: Understand the requirement

   The task should run if all upstream succeeded or if none failed but some were skipped. This means failures block the run, but skips do not.

2. Step 2: Match with trigger rules

   all_success requires all succeed (no skips allowed). none_failed allows skips but no failures. one_success runs if any succeed, which is too loose. all_done runs regardless of success or failure.

3. Step 3: Choose the correct trigger rule

   none_failed fits the requirement exactly.

4. Final Answer:

   none_failed -> Option A

5. Quick Check:

   No failures but allows skips = none_failed [OK]

Hint: Use none_failed to allow skips but no failures [OK]

Common Mistakes:

• Choosing all_success which disallows skips
• Using one_success which is too permissive
• Confusing all_done with failure conditions