Airflow

Scheduler

The Scheduler is the Airflow component that continuously parses the DAGs folder, checks each DAG’s schedule and task dependencies, and triggers task instances the moment they’re eligible to run.

What it’s doing under the hood:

Parsing — periodically re-reads DAG files to pick up changes
Scheduling — decides when a DAG run is due, based on its schedule interval
Triggering — hands eligible tasks to the executor (e.g. LocalExecutor) to actually run
State tracking — writes run and task state to the metadata database

If the scheduler is down, nothing new gets triggered — it’s the heartbeat of the whole system.