Task dependencies (>> and << operators) in Apache Airflow - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the effect of >> operator in Airflow DAGs

Given the following Airflow task dependencies:

task1 >> task2 >> task3

Which statement best describes the execution order of these tasks?

A task1 runs first, then task2, then task3

B task3 runs first, then task2, then task1

C All tasks run in parallel without order

D task2 runs first, then task1, then task3

💡 Hint

The >> operator sets the order from left to right.

The >> operator in Airflow sets a downstream dependency. So task1 runs before task2, and task2 runs before task3.

💻 Command Output

intermediate

Output of task dependencies using << operator

Consider the following Airflow task dependencies:

task3 << task2 << task1

What is the correct execution order of the tasks?

A task2 runs first, then task3, then task1

B task3 runs first, then task2, then task1

C task1 runs first, then task2, then task3

D All tasks run simultaneously

💡 Hint

The << operator sets upstream dependencies.

The << operator means the task on the right runs before the task on the left. So task1 runs before task2, and task2 runs before task3.

🔀 Workflow

advanced

Creating a diamond-shaped task dependency graph

You want to create a DAG where task1 runs first, then task2 and task3 run in parallel, and finally task4 runs after both task2 and task3 complete.

Which code snippet correctly sets these dependencies using >> and/or << operators?

A [task2, task3] >> task1 >> task4

B task1 << [task2, task3] << task4

C task4 >> [task2, task3] >> task1

D task1 >> [task2, task3] >> task4

💡 Hint

Use >> to set downstream dependencies and list to set parallel tasks.

Using task1 >> [task2, task3] >> task4 means task1 runs first, then task2 and task3 run in parallel, then task4 runs after both finish.

❓ Troubleshoot

advanced

Identifying incorrect task dependency causing cyclic error

Given the following dependencies:

task1 >> task2
 task2 >> task3
 task3 >> task1

What error will Airflow raise when parsing this DAG?

A AirflowDagCycleException due to cyclic dependency

B TaskNotFound error because task3 is missing

C No error, DAG runs successfully

D SyntaxError due to invalid operator usage

💡 Hint

Check if the dependencies form a loop.

The dependencies form a cycle: task1 -> task2 -> task3 -> task1, which Airflow does not allow and raises a cycle exception.

✅ Best Practice

expert

Choosing the best way to set multiple dependencies for clarity

You have tasks start, middle1, middle2, and end. You want start to run first, then middle1 and middle2 in parallel, and finally end after both middles finish.

Which of the following is the clearest and most maintainable way to set these dependencies using >> and/or << operators?

A start >> [middle1, middle2] >> end

B

start >> middle1
start >> middle2
middle1 >> end
middle2 >> end

C [start, middle1] >> middle2 >> end

D end << middle1 << middle2 << start

💡 Hint

Consider readability and explicitness for future maintenance.

Option B explicitly sets each dependency on its own line, making it clear and easy to maintain. Option B is concise but less explicit. Option B and D do not represent the correct order clearly.