sjyangkevin opened a new pull request, #51511:
URL: https://github.com/apache/airflow/pull/51511

   ### 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
   
   
https://github.com/apache/airflow/blob/56fbe90a8d0b56558c02d75f4ac5852e041cb058/airflow-core/src/airflow/dag_processing/collection.py#L177
   
   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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