Dag Policy raising unusual AirflowClusterPolicyError

[devgonvarun]

Apache Airflow version

3.0.4

If "Other Airflow 2 version" selected, which one?

No response

What happened?

I am using dag_policy for altering the schedule of my dags. But instead it leads to a dag import error with AirflowClusterPolicyError. I have not configured any AirflowClusterPolicyViolation in my cluster policies.

What you think should happen instead?

The dag schedule should be altered to my configured schedule in the dag_policy.

The same thing in Airflow 2.10.5 used to work without any errors.

  #Airflow 2.10.5
  def dag_policy(dag: DAG):
        dag.schedule_interval = "@once"     

How to reproduce

Create a minimal dag_policy cluster policy

  # Airflow 3.0.4 
  def dag_policy(dag: DAG):
        dag.schedule = "@once"    

Operating System

Debian GNU/Linux 12 (bookworm)

Versions of Apache Airflow Providers

No response

Deployment

Official Apache Airflow Helm Chart

Deployment details

No response

Anything else?

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[tirkarthi]

I can see below logs in the dag processor. It seems the schedule attribute is a frozen attribute that cannot be set.

airflow/task-sdk/src/airflow/sdk/definitions/dag.py

Line 393 in cdfddea

schedule: ScheduleArg = attrs.field(default=None, on_setattr=attrs.setters.frozen)

tail -n 3 ~/airflow/logs/dag_processor/latest/example_dags/example_display_name.py.log | python -m json.tool --json-lines
{
    "timestamp": "2025-08-19T14:18:25.123601Z",
    "level": "info",
    "event": "<DAG: example_display_name>",
    "chan": "stdout",
    "logger": "processor"
}
{
    "timestamp": "2025-08-19T14:18:25.114862",
    "level": "error",
    "event": "",
    "logger": "airflow.models.dagbag.DagBag",
    "error_detail": [
        {
            "exc_type": "FrozenAttributeError",
            "exc_value": "",
            "exc_notes": [],
            "syntax_error": null,
            "is_cause": false,
            "frames": [
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/models/dagbag.py",
                    "lineno": 522,
                    "name": "bag_dag"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/settings.py",
                    "lineno": 177,
                    "name": "dag_policy"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_hooks.py",
                    "lineno": 512,
                    "name": "__call__"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_manager.py",
                    "lineno": 120,
                    "name": "_hookexec"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_callers.py",
                    "lineno": 167,
                    "name": "_multicall"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_callers.py",
                    "lineno": 121,
                    "name": "_multicall"
                },
                {
                    "filename": "/home/karthikeyan/airflow/config/airflow_local_settings.py",
                    "lineno": 7,
                    "name": "dag_policy"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/attr/_make.py",
                    "lineno": 1167,
                    "name": "__setattr__"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/attr/setters.py",
                    "lineno": 35,
                    "name": "frozen"
                }
            ],
            "is_group": false,
            "exceptions": []
        }
    ]
}
{
    "timestamp": "2025-08-19T14:18:25.115501",
    "level": "error",
    "event": "Failed to bag_dag: /home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/example_dags/example_display_name.py",
    "logger": "airflow.models.dagbag.DagBag",
    "error_detail": [
        {
            "exc_type": "AirflowClusterPolicyError",
            "exc_value": "",
            "exc_notes": [],
            "syntax_error": null,
            "is_cause": false,
            "frames": [
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/models/dagbag.py",
                    "lineno": 497,
                    "name": "_process_modules"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/models/dagbag.py",
                    "lineno": 540,
                    "name": "bag_dag"
                }
            ],
            "is_group": false,
            "exceptions": []
        },
        {
            "exc_type": "FrozenAttributeError",
            "exc_value": "",
            "exc_notes": [],
            "syntax_error": null,
            "is_cause": false,
            "frames": [
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/models/dagbag.py",
                    "lineno": 522,
                    "name": "bag_dag"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/airflow-core/src/airflow/settings.py",
                    "lineno": 177,
                    "name": "dag_policy"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_hooks.py",
                    "lineno": 512,
                    "name": "__call__"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_manager.py",
                    "lineno": 120,
                    "name": "_hookexec"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_callers.py",
                    "lineno": 167,
                    "name": "_multicall"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/pluggy/_callers.py",
                    "lineno": 121,
                    "name": "_multicall"
                },
                {
                    "filename": "/home/karthikeyan/airflow/config/airflow_local_settings.py",
                    "lineno": 7,
                    "name": "dag_policy"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/attr/_make.py",
                    "lineno": 1167,
                    "name": "__setattr__"
                },
                {
                    "filename": "/home/karthikeyan/stuff/python/airflow/.venv/lib/python3.11/site-packages/attr/setters.py",
                    "lineno": 35,
                    "name": "frozen"
                }
            ],
            "is_group": false,
            "exceptions": []
        }
    ]
}

[potiuk]

Yep. Schedule cannot be modified.

[potiuk]

Converted to a discusion.