Big Data organization provides scheduler on UI or command line. User can create scheduled job to execute certain business tasks. Such tasks are set to run at specified time and date once or on recurring basis. Scheduler helps to do so conveniently.
Apache Airflow is an open-source platform for developing, scheduling, and monitoring batch-oriented workflows. The airflow works based upon Directed acyclic graph. DAG is written in Python. Python code is written for specific workflow and placed in DAG directory. Python DAG can be deployed to other Airflow.
DAG is also used to run external job. These DAG's can be called and run within Hadoop or Hive or Spark.
DAG's are python program or package. DAG's can be exported and imported into another Airflow system or Application. Imported DAG's can be made working by making compatible virtual environment and installing all prerequisite and dependent libraries to be installed.
Tasks inside DAG are used to trigger actions remotely. But remote system or application should be integrated with Airflow scheduler by any type of connectors.