Apache Workflow Terminology

Apache Workflow Terminology




TermExplanation
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 InstanceA 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.

BackfillRunning 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 APIA 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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