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I am running a number of FastAPI instances with uvicorn with python's subprocess.Popen. I have a small GUI made with PySimpleGUI with which I want to be able to close servers and restart them at will.

The first problem I encountered is that, at least in Windows, starting the uvicorn server appear to create not one, but two, new processes, and calling Popen.terminate() only closes one of these processes, which does not free up the port associated with the server. I fixed this problem using the psutil package to check what new processes have been created after I instantiate a Popen object, and track and terminate the second process with psutil.

What is still a major problem, is that calling psutil.terminate() on the process does not call the FastAPI function under @app.on_event("shutdown"). In the past, we have run all of our servers in individual terminal windows, and find that ctrl-c on those terminal windows will call the shutdown event, but I have found no other way of doing so. ctrl-c on my interface will obviously take down the interface and all the servers, and is somewhat unreliable in hitting the shutdown events for all the servers. My other idea was use psutil.send_signal(signal.CTRL_C_EVENT), but this has the same effect as calling ctrl-c in terminal.

So I am at a loss. I have seen multiple posts around saying that this is a general shortcoming of uvicorn, but have not seen anything that directly confirms my own experience or offers a solution. I also know that the "shutdown" and "startup" events in FastAPI are ported in from Starlette, and are not very well documented in either package. I have seen suggestions to use guvicorn, but my brief look into that confirmed that it is not compatible with windows. Any suggestions?

jkflowers
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1 Answers1

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TL;DR:

  • APIs are meant to be long-running processes
  • there is a whole industry around virtualizing to manage the orchestration automatically of when to start or stop a service
  • there is also "serverless" infrastructure you can hang any of your processes with you not having to spend any effort in this field as it is not meant to be a thing
  • If you still want to go against everyone else and do manage it your self you can do as this answered question
    ##### SOLUTION #####
    pid = proc.pid
    parent = psutil.Process(pid)
    for child in parent.children(recursive=True):
        child.kill()
    ##### SOLUTION END ####

A bit of explanation:

From the conception of Rest API as an architecture pattern it was meant to be awaiting always for user's requests coming over the web. it has never been the general intent to manage gracefully and develop a product to handle gracefully the shut down of something that "was meant to run forever" and we build processes to do work to keep it running 24/7/365 as an industry.

If you ever want to leverage the ability to start or stop one to many APIS simultaneously withing the same device is highly recommended d you at least go with something like containers and Kubernetes and just scripting commands against the CLI of Kubernetes for such purpose. In exchange for the extra effort you will gain process isolation from others and the base OS layer ( which will still be less effort than building all that tooling yourself on your own. My personal favorite is not doing even that and going straight with lambdas as is way easier and better in so many ways. Don't take it from me but from one of the industry-leading companies, Cloudflare and their statements on the subject

Serverless computing offers a number of advantages over traditional cloud-based or server-centric infrastructure. For many developers, serverless architectures offer greater scalability, more flexibility, and quicker time to release, all at a reduced cost.

lcarvajal
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