Apache Workflow Terminology
Apache Workflow Terminology
by PCWorkshops
| Term | Explanation |
|---|---|
| DAG | Directed Acyclic Graph — the main structure in Airflow. It defines a workflow and the order in which tasks should run. |
| Task | A single unit of work in a workflow, such as running a Python function or executing a SQL query. |
| DAG Run | One execution/instance of a DAG. If a DAG runs every day, each day's execution is a separate DAG Run. |
| Task Instance | A specific execution of a task within a particular DAG Run. |
| Scheduler | Airflow's component that monitors DAGs and determines when tasks are ready to run. |
| Executor | Determines how and where Airflow runs tasks, such as locally, in multiple processes, or on Kubernetes. |
Worker | A process or machine that actually executes Airflow tasks. |
| Webserver | Airflow's web interface, where you can view DAGs, task statuses, logs, and other information. |
| Trigger Rule | A rule that determines when a task is allowed to run based on the status of its upstream tasks. |
| Dependency | A relationship between tasks that defines their execution order. For example, A >> B means A must run before B. |
| XCom | Short for cross-communication. A mechanism for tasks to exchange small pieces of data with each other. |
| Connection | A stored configuration containing information needed to connect to an external system, such as a database or cloud service. |
| Variable | A key-value setting stored in Airflow that can be accessed by DAGs and tasks. Useful for configuration that may change. |
| Hook | A Python interface that helps Airflow communicate with external systems such as databases, APIs, or cloud platforms. |
| Sensor | A special type of task that waits for something to happen, such as a file appearing or a database record becoming available. |
| Schedule | Defines when a DAG should run, such as every day, every hour, or according to a cron expression. |
| Backfill | Running a DAG for historical dates that were not previously executed. |
| Catchup | Airflow's ability to automatically create runs for previous scheduled periods when a DAG is started or its schedule is changed. |
| TaskFlow API | A modern Airflow approach that lets you define tasks using Python functions with the @task decorator, making dependencies and data passing easier to express. |
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