Run Gunicorn with Uvicorn workers in code

main.py

""" Snippet that demonstrates how to use Gunicorn with Uvicorn workers in code.

Feel free to run:

- `python main.py` - to use uvicorn.
- `ENV=prod python main.py` - to use gunicorn with uvicorn workers.

Reference: https://docs.gunicorn.org/en/stable/custom.html
"""

import multiprocessing
import os
from typing import Any, Callable, Dict

import uvicorn
from fastapi import FastAPI
from gunicorn.app.base import BaseApplication

app = FastAPI()


@app.get("/")
async def home():
    return "Hello World!"


def number_of_workers():
    return (multiprocessing.cpu_count() * 2) + 1


class StandaloneApplication(BaseApplication):
    def __init__(self, application: Callable, options: Dict[str, Any] = None):
        self.options = options or {}
        self.application = application
        super().__init__()

    def load_config(self):
        config = {
            key: value
            for key, value in self.options.items()
            if key in self.cfg.settings and value is not None
        }
        for key, value in config.items():
            self.cfg.set(key.lower(), value)

    def load(self):
        return self.application


if __name__ == "__main__":
    if os.getenv("ENV") == "prod":
        options = {
            "bind": "%s:%s" % ("127.0.0.1", "8000"),
            "workers": number_of_workers(),
            "worker_class": "uvicorn.workers.UvicornWorker",
        }
        StandaloneApplication(app, options).run()
    else:
        uvicorn.run("main:app", reload=True)

requirements.txt

gunicorn==20.1.0
uvicorn==0.14.0
fastapi==0.66.0

Anyone who want to use factory-pattern instead, replace self.application with self.application() in L47.