Trigger rules (all_success, one_success, none_failed) in Apache Airflow - Step-by-Step Execution

Process Flow - Trigger rules (all_success, one_success, none_failed)

Start Task Execution

↓

Check Upstream Tasks Status

↓

all_success?

Yes→Run Task

↓

Skip Task

↓

one_success?

Yes→Run Task

↓

Skip Task

↓

none_failed?

Yes→Run Task

No↓

Skip Task

The task checks upstream tasks' statuses and decides to run or skip based on the trigger rule: all_success requires all upstream tasks to succeed, one_success requires at least one success, none_failed requires no failures.

Execution Sample

Apache Airflow

task = PythonOperator(
    task_id='example',
    python_callable=my_func,
    trigger_rule='all_success'
)

This task runs only if all upstream tasks succeed.

Process Table

Step	Upstream Tasks Status	Trigger Rule	Condition Met?	Action
1	Task A: success, Task B: success	all_success	Yes	Run Task
2	Task A: success, Task B: failed	all_success	No	Skip Task
3	Task A: success, Task B: failed	one_success	Yes	Run Task
4	Task A: failed, Task B: failed	one_success	No	Skip Task
5	Task A: success, Task B: skipped	none_failed	Yes	Run Task
6	Task A: success, Task B: failed	none_failed	No	Skip Task
7	Task A: skipped, Task B: skipped	none_failed	Yes	Run Task

💡 Execution stops after deciding to run or skip the task based on the trigger rule condition.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7
Upstream Statuses	N/A	success, success	success, failed	success, failed	failed, failed	success, skipped	success, failed	skipped, skipped
Trigger Rule	all_success	all_success	all_success	one_success	one_success	none_failed	none_failed	none_failed
Condition Met	N/A	Yes	No	Yes	No	Yes	No	Yes
Action	N/A	Run	Skip	Run	Skip	Run	Skip	Run

Key Moments - 3 Insights

Why does the task skip when one upstream task fails under 'all_success'?

Because 'all_success' requires every upstream task to succeed. The execution_table rows 1 and 2 show that if any upstream task fails, the condition is not met, so the task is skipped.

How can a task run if one upstream task is skipped under 'none_failed'?

The 'none_failed' rule allows the task to run as long as no upstream task failed. Skipped tasks do not count as failures. See execution_table row 5 where one task is skipped but the task still runs.

What happens if all upstream tasks fail under 'one_success'?

The task will skip because 'one_success' requires at least one success. Execution_table row 4 shows that with all failures, the condition is not met and the task is skipped.

Visual Quiz - 3 Questions

Look at the execution_table, at step 3, what is the action taken?

A Run Task

B Skip Task

C Retry Task

D Fail Task

💡 Hint

Check the 'Action' column in execution_table row 3 where upstream tasks are success and failed with 'one_success' trigger.

At which step does the 'all_success' trigger rule cause the task to skip?

A Step 1

B Step 5

C Step 2

D Step 7

💡 Hint

Look at execution_table rows with 'all_success' trigger and find where 'Condition Met?' is 'No'.

If Task B status changes from 'failed' to 'success' at step 6, what would be the new action for 'none_failed'?

A Skip Task

B Run Task

C Fail Task

D Retry Task

💡 Hint

Refer to variable_tracker for step 6 and understand that 'none_failed' requires no failures to run.

Concept Snapshot

Trigger rules decide if a task runs based on upstream tasks' states.
'all_success': run if all upstream succeed.
'one_success': run if at least one upstream succeeds.
'none_failed': run if no upstream failed (skipped allowed).
If condition not met, task is skipped.

Full Transcript

Trigger rules in Airflow control when a task runs based on the status of upstream tasks. The 'all_success' rule requires every upstream task to succeed before running the task. If any upstream task fails, the task is skipped. The 'one_success' rule runs the task if at least one upstream task succeeds; if all fail, the task is skipped. The 'none_failed' rule allows the task to run as long as no upstream task has failed; skipped tasks do not count as failures. The execution table shows different upstream task status combinations and the resulting action for each trigger rule. The variable tracker records how upstream statuses, trigger rules, conditions, and actions change step by step. Key moments clarify common confusions about why tasks run or skip under different rules. The visual quiz tests understanding by asking about specific steps and outcomes. The concept snapshot summarizes the trigger rules and their behavior in a quick reference format.