[Python] FastAPI hosted on Lambda does not serve static content

I have a FastAPI app hosted on AWS Lambda + Api Gateway using Mangum. However it seems not to be able to serve static content returning 404 error.

Here is how static directory is mounted

application = FastAPI(title="MyApp")

static_directory = Path(__file__).parent / "static"
application.mount(
f"{settings.formatted_api_stage}/static",
StaticFiles(directory=static_directory, check_dir=True),
name="static",
)


settings.formatted_api_stage corresponds to API Gateway stage like /dev in https://a123bcdefg.execute-api.eu-north-1.amazonaws.com/dev/

Mangum handler

handler = Mangum(
application, lifespan="off", api_gateway_base_path=settings.formatted_api_stage
)


AWS infra is managed using CDK

fastapi_lambda = PythonFunction(
self,
"MyLambda",
entry="../app",
index="main.py",
handler="handler",
runtime=_lambda.Runtime.PYTHON_3_13,
role=lambda_role,
memory_size=512,
timeout=Duration.seconds(5),
bundling=BundlingOptions(asset_excludes=["*.pyc", "__pycache__/"]),
)

api = apigateway.LambdaRestApi(
self,
"MyAPI",
handler=fastapi_lambda,
proxy=True,
deploy_options=apigateway.StageOptions(
stage_name=api_stage,
),
)


Then in the templates I reference static content like

<link rel="stylesheet" href="{{ url_for('static', path='/css/style.css') }}" />


But it results in a 404 error.

I can verify that static folder is packaged ok and is present in the same folder as main.py in the lambda bundle.

The app works as expected when run locally.

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