Task dependencies (>> and << operators) in Apache Airflow - Step-by-Step Execution

Process Flow - Task dependencies (>> and << operators)

Define Task A

↓

Set Dependency

↓

Execution Order

↓

Task Runs in Order

This flow shows how two tasks are defined and linked using >> or << operators to set execution order.

Execution Sample

Apache Airflow

task1 >> task2
# or
# task2 << task1

This code sets task1 to run before task2 using the >> operator (or equivalently << operator).

Process Table

Step	Action	Operator	Dependency Set	Resulting Order
1	Define task1	N/A	None	No order yet
2	Define task2	N/A	None	No order yet
3	Set dependency task1 >> task2	>>	task1 before task2	task1 runs before task2
4	Check dependency task2 << task1	<<	task1 before task2	task1 runs before task2
5	Execute tasks	N/A	task1 before task2	task1 runs first, then task2
6	End	N/A	N/A	Execution complete

💡 Execution stops after tasks run in the defined order.

Status Tracker

Variable	Start	After Step 3	After Step 5	Final
task1	Defined	Dependency set as upstream	Executed first	Completed
task2	Defined	Dependency set as downstream	Executed second	Completed

Key Moments - 3 Insights

Why does task1 >> task2 mean task1 runs before task2?

Because the >> operator sets the left task as upstream, so task2 waits for task1 to finish (see execution_table step 3).

Is task2 << task1 the same as task1 >> task2?

Yes, << sets the right task as downstream, so task2 << task1 means task1 runs before task2 (see execution_table step 4).

What happens if no dependencies are set between tasks?

Tasks run independently and may execute in any order or in parallel (see execution_table steps 1 and 2).

Visual Quiz - 3 Questions

Look at the execution table, what dependency is set at step 3?

A No dependency set

B task2 runs before task1

C task1 runs before task2

D Tasks run in parallel

💡 Hint

Check the 'Dependency Set' column at step 3 in the execution_table.

At which step do tasks actually execute in order?

A Step 2

B Step 5

C Step 3

D Step 6

💡 Hint

Look for 'Execute tasks' action in the execution_table.

If we remove the dependency operator, what changes in the execution?

A Tasks run independently or in parallel

B Tasks run in defined order

C Tasks fail to run

D Tasks run twice

💡 Hint

Refer to key_moments about no dependencies set (execution_table steps 1 and 2).

Concept Snapshot

Task dependencies in Airflow use >> and << operators.
'task1 >> task2' means task1 runs before task2.
'task2 << task1' means the same.
Without dependencies, tasks run independently.
Use these operators to control execution order.

Full Transcript

In Airflow, you define tasks and set their execution order using the >> and << operators. For example, 'task1 >> task2' means task1 must finish before task2 starts. The >> operator sets the left task as upstream, so the right task waits. The << operator works the opposite way but achieves the same result. If no dependencies are set, tasks run independently and may execute in any order or in parallel. This visual trace showed defining tasks, setting dependencies, and the resulting execution order step-by-step.