abhishekbhakat opened a new issue, #54771:
URL: https://github.com/apache/airflow/issues/54771
### Apache Airflow version
2.11.0
### If "Other Airflow 2 version" selected, which one?
_No response_
### What happened?
- A DAG defines a custom operator that accepts `start_date`/`end_date`
strings and passes them into an `args` list. The task instance is created with
a Jinja-templated string for `end_date` (and/or `start_date`).
- The operator does not list these fields in `template_fields`.
- Airflow serializes the DAG and stores the templated string (e.g., `"{{
(data_interval_end - macros.timedelta(days=4)).strftime('%Y-%m-%d') }}"`) under
the `end_date` key.
- When the scheduler later creates a DAG run and needs to deserialize, it
treats any key ending with `_date` as a datetime and force-coerces it via
`_deserialize_datetime`. Because the value is a string template,
deserialization raises a `TypeError` and the scheduler crashes.
### What you think should happen instead?
- The scheduler should never crash due to a single misconfigured/bad DAG. It
should log and skip the DAG.
- Deserialization should not attempt to coerce templated strings or
non-timestamp values for fields matching `*_date`.
- Proposed remediations (happy to submit a PR):
1) Scheduler guard: wrap `dag = self.dagbag.get_dag(dag_model.dag_id,
session=session)` in `try/except` in both `_create_dag_runs` and
`_create_dag_runs_dataset_triggered`, similar to the existing guard around
`dag.create_dagrun(...)`.
2) Deserialization guard: in
`airflow/serialization/serialized_objects.py`, change the `_date` handling to
be safe for non-numeric values, e.g.:
- Only coerce when `not isinstance(v, str)`, or
- Wrap `_deserialize_datetime(v)` in `try/except` and leave `v` as-is
on failure.
Both can be complementary. The scheduler guard provides resilience. The
deserialization guard fixes the root cause across components
(scheduler/webserver/CLI).
### How to reproduce
1) Define operators:
```py
from airflow.models.baseoperator import BaseOperator
from airflow.utils.decorators import apply_defaults
class FooOperator(BaseOperator):
# Trigger of the bug: template_fields = ("args",) is a tuple but
("args") is a string
template_fields = ("args")
@apply_defaults
def __init__(self, args=None, **kwargs):
super().__init__(**kwargs)
self.args = args
def execute(self, context):
self.log.info("Executing FooOperator with args: %s", self.args)
class BarOperator(FooOperator):
def __init__(self, start_date: str, end_date: str, **kwargs):
super().__init__(
args=["--start_date", start_date, "--end_date", end_date],
**kwargs,
)
```
2) Define DAG:
```py
from airflow.models import DAG
from airflow.operators.empty import EmptyOperator
START_DATE = "{{ (data_interval_start -
macros.timedelta(days=11)).strftime('%Y-%m-%d') }}"
END_DATE = "{{ (data_interval_end -
macros.timedelta(days=4)).strftime('%Y-%m-%d') }}"
with DAG(
dag_id="foo_bar_dag",
schedule_interval="0 7 * * *",
catchup=False,
max_active_runs=1,
) as dag:
start = EmptyOperator(task_id="start")
end = EmptyOperator(task_id="end")
foo_task = BarOperator(
task_id="foo_task",
start_date=START_DATE,
end_date=END_DATE,
)
start >> foo_task >> end
```
3) Behavior:
- On initial parse, the serialized DAG stores `end_date` as the templated
string.
- During DAG run creation, the scheduler deserializes and attempts to coerce
`end_date` via `_deserialize_datetime`, which expects a numeric timestamp,
causing `TypeError` and crashing the scheduler.
### Operating System
PRETTY_NAME="Debian GNU/Linux 12 (bookworm)" NAME="Debian GNU/Linux"
VERSION_ID="12" VERSION="12 (bookworm)" VERSION_CODENAME=bookworm ID=debian
### Versions of Apache Airflow Providers
Not applicable
### Deployment
Docker-Compose
### Deployment details
_No response_
### Anything else?
- Relation to Issue #29819 / PR #29821 (forbidden_fields):
- PR #29821 introduced a `forbidden_fields` check to prevent listing
BaseOperator constructor args (e.g., `execution_timeout`, `start_date`,
`end_date`) in `template_fields`, preventing one class of crash.
- This issue is the inverse: a templated string in a `*_date` field that
is not templated. The deserializer coerces any `*_date` value, which fails on
strings. `forbidden_fields` does not intercept this case and also forbids
adding `start_date`/`end_date` to `template_fields` to skip coercion.
- Proposal:
- Scheduler: add try/except around `get_dag(...)` in `_create_dag_runs`
and `_create_dag_runs_dataset_triggered`.
- Deserialization: guard `_date` coercion (type-check or try/except) in
both operator and DAG deserialization paths.
### Are you willing to submit PR?
- [x] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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