Cron expressions in Airflow - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the next execution time for this cron expression?

Given the cron expression 0 6 * * 1-5 in Airflow, what is the next scheduled run time if the current time is Monday 2024-06-03 05:00 UTC?

A Monday 2024-06-10 06:00 UTC

B Tuesday 2024-06-04 06:00 UTC

C Monday 2024-06-03 06:00 UTC

D Sunday 2024-06-02 06:00 UTC

💡 Hint

Remember that the cron runs at 6 AM on weekdays (Monday to Friday).

The cron expression means run at 6:00 AM on Monday through Friday. Since current time is Monday 5 AM, the next run is the same day at 6 AM.

🧠 Conceptual

intermediate

Understanding the meaning of a cron expression

What does the cron expression 30 23 15 * * mean in Airflow scheduling?

A Run at 11:30 AM on the 15th day of every month

B Run at 11:30 PM on the 15th day of every month

C Run every 15 minutes starting at 11:30 PM

D Run at 11:30 PM every day

💡 Hint

The first two numbers represent minutes and hours.

The cron fields are: minute=30, hour=23, day=15, month=any, weekday=any. So it runs once a month at 23:30 on day 15.

❓ Troubleshoot

advanced

Why does this Airflow DAG not run as expected?

An Airflow DAG has the cron schedule 0 0 31 2 *. It never runs. Why?

A February never has 31 days, so the schedule never matches

B The timezone is not set, so the DAG runs at a different time

C Airflow does not support scheduling on specific days of the month

D The cron expression syntax is invalid and causes an error

💡 Hint

Check if the date specified actually exists in the calendar.

February has at most 29 days, so day 31 never occurs. The DAG never triggers.

✅ Best Practice

advanced

Choosing a cron expression for daily midnight runs

Which cron expression is the best choice to schedule an Airflow DAG to run daily at midnight UTC?

A 0 0 * * *

B 0 24 * * *

C 0 0 1 * *

D 0 0 * * 0

💡 Hint

Midnight is hour 0, minute 0 every day.

The expression '0 0 * * *' means every day at 00:00. Option A is invalid (hour 24), C runs only on the first day of the month, D runs only on Sundays.

🔀 Workflow

expert

Order the steps to update an Airflow DAG's schedule using a cron expression

Put these steps in the correct order to update an Airflow DAG's schedule with a new cron expression.

A 3,1,2,4

B 2,1,3,4

C 1,3,2,4

D 1,2,3,4

💡 Hint

Think about editing first, then testing, then deploying, then verifying.

First edit the schedule in code, then test it, then deploy to Airflow, finally check the UI.