Authoring and Scheduling DAGs – Fundamentals Study Guide
This is the largest domain (~35% of the exam) and covers writing DAGs in Python and controlling when they run. The highest-value topics are scheduling (presets, cron, start_date), the catchup/backfill behavior, and setting task dependencies. Get comfortable with >>/<<, cron basics, and the logical-date concept and this domain scores well.
Defining a DAG
A DAG is a Python object with a dag_id (its unique identifier), a schedule, a start_date, and usually default_args (parameters applied to all its tasks). Tasks are created by instantiating operators inside the DAG.
default_args is a dictionary of shared task parameters — commonly owner, retries, retry_delay, email_on_failure — applied to every task unless overridden.
Scheduling
Presets cover common cases:
| Preset | Meaning |
|---|---|
@once | Run one time |
@hourly | Every hour (0 * * * *) |
@daily | Every day at midnight (0 0 * * *) |
@weekly / @monthly | Weekly / monthly |
None | No automatic schedule (manual/triggered only) |
Cron expressions give precise control. Field order: minute hour day-of-month month day-of-week. Example: 0 6 * * 1 = 06:00 every Monday.
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