Task failure callbacks in Apache Airflow - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the purpose of a task failure callback in Airflow?

In Airflow, what is the main purpose of setting a task failure callback function?

A To automatically restart the entire DAG run from the beginning.

B To retry the failed task immediately without any delay.

C To execute custom code automatically when a task fails, such as sending alerts or cleaning resources.

D To skip the failed task and continue the workflow without any notification.

💡 Hint

Think about what you want to happen right after a task fails.

A task failure callback lets you run custom code when a task fails, like sending an email alert or logging extra info. It does not retry or skip tasks automatically.

💻 Command Output

intermediate

Output of a task failure callback function logging failure info

Given this Airflow task failure callback function, what will be printed when a task fails?

Apache Airflow

def failure_callback(context):
    task_instance = context['task_instance']
    print(f"Task {task_instance.task_id} failed at {task_instance.end_date}")

A Task <task_id> succeeded at <timestamp>

B Task <task_id> failed at <timestamp>

C Error: 'end_date' attribute not found

D No output is printed

💡 Hint

Look at what the print statement outputs using the context dictionary.

The callback prints the task ID and the time it ended, which is when it failed.

❓ Configuration

advanced

Correct way to assign a failure callback to an Airflow task

Which code snippet correctly assigns a failure callback function named notify_failure to an Airflow PythonOperator task?

A task = PythonOperator(task_id='task1', python_callable=my_func, on_failure_callback=notify_failure)

B task = PythonOperator(task_id='task1', python_callable=my_func, failure_callback=notify_failure)

C task = PythonOperator(task_id='task1', python_callable=my_func, on_fail_callback=notify_failure)

D task = PythonOperator(task_id='task1', python_callable=my_func, on_failure=notify_failure)

💡 Hint

Check the exact parameter name for failure callbacks in Airflow operators.

The correct parameter to assign a failure callback is on_failure_callback. Other options are invalid parameter names.

❓ Troubleshoot

advanced

Why is the failure callback not triggered on task failure?

You assigned a failure callback to a task, but it never runs when the task fails. What is the most likely reason?

A Failure callbacks only run if the DAG run succeeds.

B The task is marked as <code>retries=0</code>, so failure callbacks are skipped.

C The failure callback function must be decorated with <code>@task_failure</code> to work.

D The failure callback function is not passed as <code>on_failure_callback</code> parameter to the task.

💡 Hint

Check how the failure callback is assigned to the task.

If the failure callback is not assigned using the on_failure_callback parameter, Airflow will not know to run it on failure.

🔀 Workflow

expert

Order of execution when a task fails with a failure callback

Arrange the steps in the correct order when an Airflow task fails and a failure callback is set.

A 1,2,3,4

B 3,1,2,4

C 2,1,3,4

D 1,3,2,4

💡 Hint

Think about what happens first: failure, marking state, then callback.

First the task fails, then Airflow marks it failed, then it calls the failure callback, which performs actions.