BigData / Apache Airflow Interview Questions

What is the ExternalTaskSensor in Airflow?

The ExternalTaskSensor waits for a task in another DAG (or the DAG itself) to reach a target state (default: success) before proceeding. This enables cross-DAG dependencies without tight coupling.

from airflow.sensors.external_task import ExternalTaskSensor

wait = ExternalTaskSensor(
    task_id='wait_for_upstream',
    external_dag_id='upstream_dag',
    external_task_id='final_task',
    mode='reschedule',
    timeout=3600
)

The sensor matches runs by execution_date by default. Use execution_date_fn or execution_delta when the upstream DAG runs on a different schedule.

Take quiz

How does ExternalTaskSensor match runs in the external DAG by default? By matching the execution_date

✓ Correct! Well done.

By matching the run_id

✗ Try again if not.

It always polls the most recent run

✗ Try again if not.

More Related questions...

What is Apache Airflow? What is a DAG in Apache Airflow? What are Operators in Apache Airflow? What is the Airflow Scheduler? What are the main components of Apache Airflow? What is an Executor in Airflow and what types are available? What is an Airflow Connection? What is an Airflow Variable? What is XCom in Airflow and how is it used? What are Hooks in Apache Airflow? What is the difference between a DAG Run and a Task Instance in Airflow? What are Sensors in Apache Airflow? What is catchup in Airflow and how does it work? What is backfilling in Apache Airflow? What is the TaskFlow API in Airflow? What is the difference between schedule_interval and timetable in Airflow? What is a SubDAG and why is it generally discouraged? What is a TaskGroup in Airflow? What is branching in Airflow and how is BranchPythonOperator used? What are trigger rules in Airflow? What is the Airflow metadata database and what does it store? How does the CeleryExecutor work in Airflow? What is the KubernetesExecutor and what are its benefits? What are Pools in Apache Airflow? What are Airflow Providers? What is dynamic task mapping in Airflow? What is the difference between depends_on_past and wait_for_downstream in Airflow? What is the Airflow Web UI and what can you do with it? What are Airflow task states and what do they mean? What are retries and retry_delay in Airflow tasks? What is a Deferrable Operator (async operator) in Airflow? What are Airflow Plugins? How does Airflow handle templating and macros? What is idempotency in the context of Airflow tasks? What are best practices for writing efficient Airflow DAGs? What is the ExternalTaskSensor in Airflow? What is the KubernetesPodOperator in Airflow? What are SLAs in Apache Airflow and how are they configured? How does Airflow handle task concurrency and parallelism? What is an Airflow Dataset and how does data-driven scheduling work? What is the difference between Airflow and Apache Spark? How do you deploy Apache Airflow using Docker Compose? What is Airflow on Kubernetes (KEDA) autoscaling? What is the SparkSubmitOperator in Airflow? What is Managed Airflow (MWAA) on AWS? How does Airflow handle secrets management? What is the difference between PythonOperator and PythonVirtualenvOperator? What is the Grid view in Airflow 2.x? What are common Airflow anti-patterns to avoid? What is Airflow 2 vs Airflow 1 — key differences?

Show more question and Answers...

Apache Parquet Interview Questions

Comments & Discussions

Hadoop basics 33 Hadoop MapReduce 7 Apache Spark 23 TensorFlow 6 Data pipeline interview questions 12 Splunk Interview Questions 23 Tableau Interview Questions 52 Apache Airflow Interview Questions 50 Apache Parquet Interview Questions 30 Data Lake Interview questions 40

Recently added questions

What is parameter binding in MyBatis? How do you integrate MyBatis with Spring Boot? What is a SqlSessionFactory in MyBatis? How do you write a basic SELECT statement in MyBatis? What is the difference between #{} and ${} in MyBatis? What is MyBatis-Spring? What is MyBatis? What is the difference between MyBatis and Hibernate? What is a Mapper interface in MyBatis? What is a Mapper XML file? What is result mapping? What are the supported statement types in MyBatis? What is a resultMap? How do you configure a data source in MyBatis? What is the mybatis-config.xml file used for? Explain how pagination is typically implemented in MyBatis? What is the purpose of MyBatis? What are the key features of MyBatis? What is a SqlSession in MyBatis? What is dynamic SQL in MyBatis?

	Interviews Questions Java Spring Hibernate DevOps Testing API BigData Web Erlang AI Database Integration Cloud Python Scala Tools Golang SAP	About Javapedia.net Javapedia.net is for Java and J2EE developers, technologist and college students who prepare of interview. Also this site includes many practical examples. This site is developed using J2EE technologies by Steve Antony, a senior Developer/lead at one of the logistics based company. Follow Javapedia updates
	contact: javatutorials2016[at]gmail[dot]com
Kindly consider donating for maintaining this website. Thanks.
	Copyright © 2026, javapedia.net, all rights reserved. Privacy Policy · Terms of Service.