RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt

# (1)
COPY ./main.py /code/

# (2)
CMD ["fastapi", "run", "main.py", "--port", "80"]
```

1. Copy the `main.py` file to the `/code` directory directly (without any `./app` directory).

2. Use `fastapi run` to serve your application in the single file `main.py`.