(python) FastAPI background tasks not supported

[CGarces]

Hi!

I'm trying to port this code to lambda using lambda web adapter.

@router.post("/node/", response_model=NodeCreateResponse, status_code=201)
async def create_node_endpoint(background_tasks: BackgroundTasks, node_data: NodeInfoPayload = Body(...)):
    try:
        node =await crud.create_node(node_data.payload)
        background_tasks.add_task(crud.create_connections, node)
        return  JSONResponse(content={"payload":{"id":node.uid,"name":node.name}}, status_code=201)
    except HTTPException as e:
        raise e
    except Exception as e:

        return JSONResponse(content={"error": str(e)}, status_code=400)

After the return function the lambda is finished so the background tasks is never executed.

I assume that this not is supported ¿there is any other options without change too much the source code?

[bnusunny]

Lambda freezes the execution environment after the handler function returns. So the backup jobs won't work.

However, you should be able to get around that with an internal extension. Lambda will wait until the internal extension finishes before freezing the execution environment.

It is a good experiment to create a package to integrate FastAPI background tasks with Lambda internal extension.

[CGarces]

"Lambda internal extension"
Can you point me to some documentation?
I'm checking this
https://github.com/garysassano/cdk-aws-lambda-internal-extension

But I'm not sure if is the correct way (it's a 2 years old repo).
Fell free to convert this issue as discussion, because is not an issue.

[bnusunny]

That uses a wrapper script, which is not useful in this case.

Let me create an example for this.

[bnusunny]

Before I complete the example, you can check out this Rust Lambda example: https://github.com/awslabs/aws-lambda-rust-runtime/tree/main/examples/extension-internal-flush

[bnusunny]

PR is created: #408

[bnusunny]

The example is here: https://github.com/awslabs/aws-lambda-web-adapter/tree/main/examples/fastapi-background-tasks