SLA misses and notifications in Apache Airflow - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding SLA Misses in Airflow

What happens in Airflow when a task misses its SLA?

A Airflow immediately stops the entire DAG run and marks it as failed.

B Airflow triggers an SLA miss callback and logs the event but does not stop the DAG run.

C Airflow retries the task automatically regardless of retry settings.

D Airflow ignores the SLA miss and continues without any notification.

💡 Hint

Think about how Airflow handles SLA misses without interrupting the workflow.

When a task misses its SLA, Airflow triggers an SLA miss callback and logs the event. It does not stop the DAG run or retry the task automatically. This allows the workflow to continue while notifying about the delay.

💻 Command Output

intermediate

SLA Miss Notification Email Content

Given the following SLA miss callback function in Airflow, what will be the subject line of the notification email sent?

def sla_miss_callback(dag, task_list, blocking_task_list, slas, blocking_tis):
    return f"SLA Miss Alert: DAG {dag.dag_id} missed SLA for tasks {', '.join(task_list)}"

# Assume dag.dag_id = 'data_pipeline', task_list = ['task1', 'task2']

A SLA Miss Alert: DAG data_pipeline missed SLA for tasks task1, task2

B Alert: SLA missed for data_pipeline tasks task1 and task2

C SLA Missed: data_pipeline task1 task2

D Notification: SLA miss detected in DAG data_pipeline

💡 Hint

Look carefully at the string formatting in the callback function.

The callback function returns a formatted string with the DAG ID and the list of tasks that missed the SLA, joined by commas. This exact string is used as the email subject.

❓ Configuration

advanced

Configuring SLA Miss Email Notifications

Which Airflow configuration setting must be enabled to send email notifications on SLA misses?

A sla_miss_callback must be set and email backend configured

B send_sla_notifications = True in airflow.cfg

C email_on_sla_miss = True in DAG definition

D enable_sla_miss_email = True in airflow.cfg

💡 Hint

Think about what is required beyond just a config flag to send emails.

Airflow requires a defined sla_miss_callback function and a properly configured email backend to send SLA miss notifications. There is no direct config flag like 'enable_sla_miss_email'.

❓ Troubleshoot

advanced

Troubleshooting Missing SLA Notifications

You configured SLA miss notifications in Airflow, but no emails are received when SLAs are missed. What is the most likely cause?

A The SMTP server settings in airflow.cfg are incorrect or missing.

B The DAG has no SLA defined on any tasks.

C The SLA miss callback function is not defined or not assigned in the DAG.

D All of the above.

💡 Hint

Consider all parts needed for SLA notifications to work.

Missing SLA notifications can be caused by no SLA defined, missing callback function, or incorrect email server settings. All these must be correctly set for notifications to work.

🔀 Workflow

expert

SLA Miss Handling Workflow in Airflow

Order the steps Airflow takes when a task misses its SLA.

A 1,3,2,4

B 1,2,4,3

C 1,2,3,4

D 2,1,3,4

💡 Hint

Think about detection, callback, notification, and workflow continuation order.

First, Airflow detects the SLA miss, then triggers the callback, which sends notifications or logs the event, and finally the DAG run continues without stopping.

Practice

1. What does setting an sla parameter on an Airflow task do?

easy

A. It defines a time limit; if the task runs longer, it triggers an SLA miss.

B. It sets the maximum retries for the task.

C. It schedules the task to run at a specific time.

D. It disables the task from running automatically.

Solution

1. Step 1: Understand the purpose of sla in Airflow tasks

   The sla parameter sets a time limit for task execution.

2. Step 2: Identify what happens when the limit is exceeded

   If the task runs longer than the sla time, Airflow marks it as an SLA miss.

3. Final Answer:

   It defines a time limit; if the task runs longer, it triggers an SLA miss. -> Option A

4. Quick Check:

   sla sets time limit = C [OK]

Hint: Remember SLA means max allowed time for task [OK]

Common Mistakes:

• Confusing SLA with retry count
• Thinking SLA schedules task start time
• Assuming SLA disables tasks

2. Which of the following is the correct way to define an SLA of 30 minutes on a task in Airflow?

easy

A. sla='30 minutes'

B. sla=30

C. sla=timedelta(minutes=30)

D. sla='00:30:00'

Solution

1. Step 1: Recall the correct data type for sla

   The sla parameter expects a datetime.timedelta object.

2. Step 2: Identify the correct syntax for 30 minutes timedelta

   timedelta(minutes=30) correctly creates a 30-minute duration.

3. Final Answer:

   sla=timedelta(minutes=30) -> Option C

4. Quick Check:

   sla uses timedelta object = B [OK]

Hint: Use timedelta for time durations in Airflow [OK]

Common Mistakes:

• Using string instead of timedelta
• Passing integer without timedelta
• Using incorrect string format

3. Given this DAG snippet, what will happen if task1 runs longer than 10 minutes?

from datetime import timedelta
from airflow import DAG
from airflow.operators.dummy import DummyOperator
from airflow.utils.dates import days_ago

def sla_miss_callback(dag, task_list, blocking_task_list, slas, session=None):
    print('SLA missed!')

dag = DAG('sla_example', start_date=days_ago(1))

task1 = DummyOperator(
    task_id='task1',
    dag=dag,
    sla=timedelta(minutes=10)
)

dag.sla_miss_callback = sla_miss_callback

medium

A. The sla_miss_callback function will print 'SLA missed!' when the SLA is missed.

B. Nothing happens because DummyOperator ignores SLA.

C. The task will automatically retry until it finishes within 10 minutes.

D. Airflow will fail the DAG immediately.

Solution

1. Step 1: Understand SLA miss callback usage

   The DAG-level sla_miss_callback is called when any task misses its SLA.

2. Step 2: Identify what the callback does

   The callback prints 'SLA missed!' when triggered by a task exceeding its SLA.

3. Final Answer:

   The sla_miss_callback function will print 'SLA missed!' when the SLA is missed. -> Option A

4. Quick Check:

   SLA miss triggers callback print = A [OK]

Hint: SLA miss triggers callback, not retries or failure [OK]

Common Mistakes:

• Thinking SLA causes retries automatically
• Assuming DummyOperator ignores SLA
• Believing DAG fails immediately on SLA miss

4. You wrote this code to notify on SLA misses but no notification happens:

def notify_sla_miss(dag, task_list, blocking_task_list, slas, session=None):
    send_email('[e-mail]', 'SLA Missed')

dag = DAG('sla_notify', start_date=days_ago(1), sla_miss_callback=notify_sla_miss)

task = DummyOperator(task_id='task', dag=dag, sla=timedelta(minutes=5))

What is the likely reason notifications are not sent?

medium

A. DummyOperator does not support SLA misses.

B. SLA miss callback must be set on the task, not the DAG.

C. The SLA time must be set in seconds, not minutes.

D. The send_email function is not defined or imported.

Solution

1. Step 1: Check the callback function implementation

   The callback calls send_email but no import or definition is shown.

2. Step 2: Understand Airflow's email sending

   Airflow requires proper email function or operator; undefined send_email causes failure silently.

3. Final Answer:

   The send_email function is not defined or imported. -> Option D

4. Quick Check:

   Undefined email function blocks notification = D [OK]

Hint: Ensure email functions are imported or use Airflow email operators [OK]

Common Mistakes:

• Setting callback on DAG instead of task (both valid but DAG preferred)
• Wrong SLA time units
• Assuming DummyOperator ignores SLA

5. You want to send a custom Slack message when any task misses its SLA in your DAG. Which approach correctly implements this?

hard

A. Set sla on tasks and add a SlackOperator as a downstream task to notify SLA misses.

B. Define a sla_miss_callback function that uses Slack API and assign it to the DAG's sla_miss_callback parameter.

C. Use on_failure_callback on tasks to send Slack messages when SLA is missed.

D. Configure Airflow to send Slack notifications by setting sla to the Slack channel name.

Solution

1. Step 1: Understand how SLA miss notifications work

   SLA misses trigger the sla_miss_callback function assigned to the DAG or task.

2. Step 2: Identify correct way to send Slack message on SLA miss

   Implement a callback function that calls Slack API and assign it to DAG's sla_miss_callback.

3. Final Answer:

   Define a sla_miss_callback function that uses Slack API and assign it to the DAG's sla_miss_callback parameter. -> Option B

4. Quick Check:

   SLA miss callback with Slack API = A [OK]

Hint: Use sla_miss_callback with Slack API for notifications [OK]

Common Mistakes:

• Using on_failure_callback instead of sla_miss_callback
• Trying to notify via downstream tasks
• Misconfiguring sla parameter as Slack channel