armandduijn opened a new issue, #40745:
URL: https://github.com/apache/airflow/issues/40745
### Apache Airflow version
2.9.2
### If "Other Airflow 2 version" selected, which one?
_No response_
### What happened?
The ExternalTaskSensor in deferrable mode doesn't throw an error if the
external DAG doesn't exist. Setting `check_existence=True` doesn't have an
effect.
### What you think should happen instead?
The task should immediately fail instead of staying in the deferred state.
### How to reproduce
The code below implements a DAG with two ExternalTaskSensor tasks. One task
is set to be deferred and the other one is old non-deferred way.
When running the DAG, the `regular_sensor` task will immediately retry and
eventually fail, while the `defer_sensor` task will remain deferred.
```python
from datetime import datetime
from airflow import DAG
from airflow.sensors.external_task import ExternalTaskSensor
with DAG(
"Test",
default_args={ "start_date": datetime(2024, 7, 11) }
) as dag:
ExternalTaskSensor(
task_id="defer_sensor",
external_dag_id="FakeDAG",
check_existence=True,
deferrable=True,
)
ExternalTaskSensor(
task_id="regular_sensor",
external_dag_id="FakeDAG",
check_existence=True,
deferrable=False,
)
```
### Operating System
Windows
### Versions of Apache Airflow Providers
_No response_
### Deployment
Docker-Compose
### 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
- [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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