tomyedwab opened a new issue #16764: URL: https://github.com/apache/airflow/issues/16764
**Apache Airflow version**: 2.0.1 **Environment**: - **Cloud provider or hardware configuration**: Various (GCP & local Python) - **OS** (e.g. from /etc/os-release): Various (linux, OSX) **What happened**: I read the following documentation about Task Groups: https://airflow.apache.org/docs/apache-airflow/stable/concepts/index.html https://www.astronomer.io/guides/task-groups From this documentation it seemed that dependencies between Task Groups are possible, which is a really nice feature for complex DAGs where adding a task to one group no longer involves updating the dependencies of tasks in downstream groups. I implemented a Task Group with dependency relationships to start and end dummy tasks. However when the DAG was run the start, end, and first task of the group all ran simultaneously. It took me a while to see what I was doing wrong, which was that I was adding the group dependencies *before* adding tasks to the group. One big source of confusion here is that the Graph View of the DAG does show connecting lines from the start/end tasks to the Task Group, so it __looks__ like there should be dependencies when there aren't any. The Tree View however shows no such dependencies. **What you expected to happen**: I would expect the Graph View to show the same dependencies as the Tree View, and not show dependencies that aren't actually there. My mental model from reading the documentation was that the dependencies were set on the group, whereas it seems as if the dependencies are actually set on whatever tasks happen to be in the group at the time the dependency is added. If this is indeed how Task Groups are intended to work it might be worth clarifying this somewhere in the documentation and not just rely on examples that do the right thing. **How to reproduce it**: Here is an example that shows what how my DAG was laid out: ``` with DAG( 'task_group_test', default_args=default_args, description='Task Group Test', start_date=datetime(2021, 7, 1), schedule_interval=None) as dag: start = DummyOperator(task_id='start') end = DummyOperator(task_id='end') with TaskGroup('tg') as taskgroup: start >> taskgroup >> end task1 = PythonOperator(task_id='hello1', python_callable=_print_hello) task2 = PythonOperator(task_id='hello2', python_callable=_print_hello) task1 >> task2 ``` Here is what I see in the Graph View:  Here is what I see in the Tree View:  If I move the `start >> taskgroup >> end` line below the `task1 >> task2` line the Graph View is exactly identical but the Tree View matches my expectation:  -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
