Execution API health route (empty path) breaks api-server, dag-processor startup under FastAPI 0.137.0

[shanicad]

Under which category would you file this issue?

Core

Apache Airflow version

3.2.2

What happened and how to reproduce it?

What happened

The airflow api-server, airflow-dag-processor crash-loops on startup when FastAPI 0.137.0 is installed.

apache-airflow-core declares an uncapped FastAPI lower bound:

fastapi[standard-no-fastapi-cloud-cli]>=0.129.0

(https://github.com/apache/airflow/blob/3.2.2/airflow-core/pyproject.toml#L98)

So any install that doesn't apply the constraints file (custom base images, pip install without -c, etc.) resolves FastAPI to the latest 0.137.0 and breaks.

FastAPI 0.137.0 changed include_router from eager inclusion (child paths concatenated with the prefix immediately) to live/lazy inclusion (the original nested router is kept and walked recursively). The empty-prefix + empty-path check now descends into nested routers and rejects the execution API's health route, which is registered with an empty path (@router.get("") in airflow/api_fastapi/execution_api/routes/health.py) and included via cadwyn with no prefix.

Traceback:

File ".../airflow/api_fastapi/execution_api/app.py", line 263, in create_task_execution_api_app
    app.generate_and_include_versioned_routers(execution_api_router)
File ".../cadwyn/applications.py", line 365, in generate_and_include_versioned_routers
    self._latest_version_router.include_router(router)
File ".../fastapi/routing.py", line 2442, in include_router
    raise FastAPIError(
fastapi.exceptions.FastAPIError: Prefix and path cannot be both empty (path operation: health)

It's purely the FastAPI version: with 0.136.3 (everything else identical — airflow 3.2.2, starlette 1.3.1, cadwyn 7.0.0) the api-server starts fine; with 0.137.0 it crash-loops.

Related:

• cadwyn reports the same FastAPI 0.137.0 breakage (different symptom — /docs 404): Fastapi 0.137.0 breaks cadwyn docs zmievsa/cadwyn#378

How to reproduce

1. Install Airflow 3.2.2 without the constraints file so FastAPI floats to latest:

   pip install "apache-airflow==3.2.2"
   pip install "fastapi==0.137.0"
   

2. Run airflow api-server.
3. Startup fails with FastAPIError: Prefix and path cannot be both empty (path operation: health).

Workaround: pip install "fastapi==0.136.3".

Deployment details

api-server on a custom image whose base bundles FastAPI from the uncapped >=0.129.0 range; a rebuild drifted FastAPI 0.136.3 → 0.137.0 and triggered the crash.

What you think should happen instead?

The api-server should start with any FastAPI allowed by the dependency spec. Either:

1. Re-add an upper bound until compatible, e.g. fastapi[...]>=0.129.0,<0.137; and/or
2. Give the execution-API health route a non-empty path (@router.get("/") instead of @router.get("")) so it tolerates FastAPI 0.137.0's stricter nested router-inclusion check.

Operating System

Linux

Deployment

Official Apache Airflow Helm Chart

Apache Airflow Provider(s)

No response

Versions of Apache Airflow Providers

No response

Official Helm Chart version

Not Applicable

Kubernetes Version

No response

Helm Chart configuration

No response

Docker Image customizations

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

[boring-cyborg]

Thanks for opening your first issue here! Be sure to follow the issue template! If you are willing to raise PR to address this issue please do so, no need to wait for approval.

[Revanth14]

I can take a look at this and open a PR. I’ll start with making the execution API health route compatible with FastAPI 0.137.0 and adding a regression test.