Will sending SIGHUP to "fastapi run" process result in graceful restart?

[estan]

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Example Code

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Description

If I send a SIGHUP signal to the "fastapi run" process, will it result in a graceful restart?

With graceful I mean a restart where there's no risk of a request being "lost"? (e.g. like my reverse proxy responding with a 500 Internal Server Error).

I know that "fastapi run" internally uses uvicorn, and I know that the uvicorn docs at https://www.uvicorn.org/server-behavior/#graceful-process-shutdown says:

Graceful process shutdowns are particularly important during a restart period. During this period you want to:

• Start a number of new server processes to handle incoming requests, listening on the existing socket.
• Stop the previous server processes from listening on the existing socket.
• Close any connections that are not currently waiting on an HTTP response, and wait for any other connections to finalize their HTTP responses.
• Wait for any background tasks to run to completion, such as occurs when the ASGI application has sent the HTTP response, but the asyncio task has not yet run to completion.

Uvicorn handles process shutdown gracefully, ensuring that connections are properly finalized, and all tasks have run to completion. During a shutdown period Uvicorn will ensure that responses and tasks must still complete within the configured timeout periods.

But I'm unsure if all the steps in this description applies to uvicorn itself, or only when combining it with gunicorn as a process manager, and, if the former, if it applies to "fastapi run".

Operating System

Linux

Operating System Details

Ubuntu 24.04.3 LTS

Python Version

3.12.3

Additional Context

I use fastapi-cli 0.0.12 and will use Caddy as reverse proxy for my app

[estan]

I did an experiment running fastapi run --workers 2. The log said:

      INFO   Started parent process [70527]
      INFO   Started server process [70530]
      INFO   Waiting for application startup.
      INFO   Application startup complete.
      INFO   Started server process [70529]
      INFO   Waiting for application startup.
      INFO   Application startup complete.

I then sent SIGHUP signal to the fastapi run process. The log then said:

      INFO   Received SIGHUP, restarting processes.
      INFO   Terminated child process [70529]
      INFO   Waiting for child process [70529]
      INFO   Shutting down
      INFO   Waiting for application shutdown.
      INFO   Application shutdown complete.
      INFO   Finished server process [70529]
      INFO   Terminated child process [70530]
      INFO   Waiting for child process [70530]
      INFO   Shutting down
      INFO   Waiting for application shutdown.
      INFO   Application shutdown complete.
      INFO   Finished server process [70530]
      INFO   Started server process [70855]
      INFO   Waiting for application startup.
      INFO   Application startup complete.
      INFO   Started server process [70856]
      INFO   Waiting for application startup.
      INFO   Application startup complete.

I.e. it first tore down the server processes 70529 and 70530, and then started server processes 70855 and 70856.

So I guess this is not a graceful restart and that in between INFO Finished server process [70530] and INFO Started server process [70855] above, requests could be lost?