Motivation

As described in #49651, when the access control for a DAG is set to an non-exist role, the DAG import error show up in Airflow UI for a while and then disappear. The update is to fix this issue, and let the import error persist in the metadata DB until the DAG is updated with a correct access control setting.

Close #49651

What is the issue

When the DAG's access control is set to a non-exist role, the following process will raise an Exception "Failed to write serialized DAG dag_id=...". So, how this exception is triggered?

1. dag_was_updated will be True when the first time SerializedDagModel.write_dag write the serialized DAG to the database.
2. when dag_was_updated is True, _sync_dag_perms will be triggered to sync DAG specific permissions. At the moment, it detects that the role doesn't exist, and raise an error, resulting in the exception.
3. This exception will be captured, and being logged as an import error temporary in the DB, and show up in the UI.

From my understanding, this sync process will run for every MIN_SERIALIZED_DAG_UPDATE_INTERVAL. So, what happen in the second run.

1. dag_was_updated will be False since the DAG code is not updated.
2. In this case, _sync_dag_perms will NOT BE TRIGGERED even though in the access control is set incorrectly in the DAG code.
3. Therefore, no exception will be raised, and no import error will be logged. Therefore, the import error is removed from the DB, as well as from the UI.

What is the fix

In the current state, _sync_dag_perms runs only when the DAG is updated (i.e., dag_was_updated is True). This can be more performant because it doesn't run for all the DAGs. However, it cannot properly handle the sync for permissions. Therefore, the current fix is to make _sync_dag_perms run for all the DAGs during the DAG sync process. I understand it might not be an ideal fix, but I wasn't able to find a better solution due to my limited understanding on the code. I would really appreciate if anyone could suggest some ideas to further improve it.

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