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 /

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.