I had a similar issue on my Mac, and it was due to mono not being installed (https://www.mono-project.com/download/stable/) and also not set-up on my path. via export PATH=/Library/Frameworks/Mono.framework/Versions/Current/bin/:${PATH}
This was causing the debugger to throw the same 500 errors.

@Msordet did you find any solution to this problem?

same here..
Did you solve it?

I solve it.

https://github.com/mcauto/todo-list-fastapi/tree/master

I was able to debug by following the docs in VS Code but instead of adding debugpy.listen(5678) as they have suggested, I put in debugpy.listen(("0.0.0.0", 5678))

My docker-compose setup is based on the full-stack-fastapi-postgresql cookiecutter provided by tiangolo.

There's no need for Python code: https://github.com/Kludex/fastapi-docker-debug

@Kludex I used your solution as a template and I can debug and hit breakpoints, thank you.

Launch.json

{
  "configurations": [
    {
      "name": "Python: Remote Attach",
      "type": "python",
      "request": "attach",
      "port": 5678,
      "host": "localhost",
      "pathMappings": [
        {
          "localRoot": "${workspaceFolder}/app",
          "remoteRoot": "/app"
        }
      ]
    }
  ]
}

docker-compose.debug.yml

version: "3.3"
services:
  backend:
    environment:
      - SERVER_NAME=${DOMAIN?Variable not set}
      - SERVER_HOST=https://${DOMAIN?Variable not set}
      # Allow explicit env var override for tests
      - SMTP_HOST=${SMTP_HOST}    
    env_file:
      - .env
    build:
      context: ./backend
      dockerfile: backend.dockerfile
      args:
        INSTALL_DEV: ${INSTALL_DEV-false}
    command:
      [
        "sh",
        "-c",
        "pip install debugpy && python -m debugpy --wait-for-client --listen 0.0.0.0:5678 -m uvicorn app.main:app --reload --host 0.0.0.0 --port 8000",
      ]
    volumes:
      - ./backend/app:/app
    ports:
      - 8000:8000
      - 5678:5678


networks:
  traefik-public:
    # For local dev, don't expect an external Traefik network
    external: false

Command to run backend in debug mode

docker-compose -f docker-compose.debug.yml up

You're welcome. 😗

@tiangolo @Kludex suggestion to close this issue (or move it to a discussion). I'm reading this more like a VSCode/debugging setup issue, rather than something directly related to FastAPI code base.

Thanks for the discussion everyone!

And nice job @Kludex ! 🚀

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.