Task documentation and tags in Apache Airflow - Step-by-Step Execution

Process Flow - Task documentation and tags

Define Task

↓

Add Documentation

↓

Add Tags

↓

Run DAG

↓

View Docs & Tags in UI

This flow shows how to define a task, add documentation and tags, then run the DAG to see docs and tags in Airflow UI.

Execution Sample

Apache Airflow

from airflow import DAG
from airflow.operators.bash import BashOperator
from datetime import datetime

dag = DAG('example_dag', start_date=datetime(2024,1,1))

task = BashOperator(
    task_id='print_date',
    bash_command='date',
    dag=dag,
    doc_md='''This task prints the current date.''',
    tags=['example', 'date']
)

Defines a BashOperator task with documentation and tags inside a DAG.

Process Table

Step	Action	Code Line	Result
1	Import modules	from airflow import DAG from airflow.operators.bash import BashOperator from datetime import datetime	Modules ready
2	Create DAG object	dag = DAG('example_dag', start_date=datetime(2024,1,1))	DAG 'example_dag' created
3	Define task with doc and tags	task = BashOperator(..., doc_md='This task prints the current date.', tags=['example', 'date'])	Task 'print_date' created with docs and tags
4	Run DAG in Airflow UI	airflow dags trigger example_dag	DAG run started, task executes
5	View task docs in UI	Open Airflow UI > DAGs > example_dag > print_date > Documentation tab	Documentation visible: 'This task prints the current date.'
6	View task tags in UI	Open Airflow UI > DAGs > example_dag > Tags column	Tags visible: 'example', 'date'
7	End	N/A	Task docs and tags successfully applied and visible

💡 All steps completed, task documentation and tags are set and visible in Airflow UI

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
dag	None	DAG object created	DAG object unchanged	DAG object unchanged
task	None	None	BashOperator task with doc and tags	Task ready to run with docs and tags

Key Moments - 3 Insights

Why does the task documentation not appear if I forget to use 'doc_md'?

The execution_table row 3 shows that documentation is added via 'doc_md'. Without it, Airflow has no text to display in the docs tab.

Can I add multiple tags to a task and how are they shown?

Yes, as shown in row 3 and 6, tags are a list of strings. They appear in the Airflow UI tags column separated by commas.

Does adding tags affect task execution?

No, tags are metadata only. The execution_table row 4 shows task runs normally regardless of tags.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the task created with documentation and tags?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'Action' column in execution_table row 3 for task creation details.

According to variable_tracker, what is the value of 'task' after step 3?

A DAG object

B BashOperator task with doc and tags

C None

D String with documentation text

💡 Hint

Look at variable_tracker row for 'task' under 'After Step 3' column.

If you remove the 'tags' list from the task, what changes in the execution_table?

A Step 6 will show no tags in UI

B Step 3 will not create the task

C Step 4 will fail to run the DAG

D Step 5 will not show documentation

💡 Hint

Refer to execution_table rows 3 and 6 about tags presence and UI display.

Concept Snapshot

Task documentation and tags in Airflow:
- Use 'doc_md' parameter in task to add markdown docs.
- Use 'tags' parameter as list of strings for metadata.
- Docs appear in Airflow UI under task Documentation tab.
- Tags appear in DAGs list and task details.
- Tags do not affect task execution.

Full Transcript

This visual execution shows how to add documentation and tags to an Airflow task. First, we import necessary modules and create a DAG object. Then, we define a BashOperator task with the 'doc_md' parameter to add documentation and 'tags' parameter to add tags. When the DAG runs, the task executes normally. In the Airflow UI, the documentation is visible under the task's Documentation tab, and tags appear in the DAGs list and task details. Tags are metadata only and do not affect execution. The variable tracker confirms the task object holds the documentation and tags after creation. Key moments clarify common confusions about missing docs, multiple tags, and execution impact. The quiz tests understanding of when docs and tags are set and their UI visibility.