FastAPI Uvicorn logging in Production

Hello 🙋‍♂️,

Running a ⏩FastAPI ⏩ application in production is very easy and fast, but along the way some Uvicorn logs are lost.

In this article I will discuss how to write a custom UvicornWorker and to centralize your logging configuration into a single file.

To keep things as simple as possible I’ve put all my code in a single Python file.

main.py

import uvicorn as uvicorn
from fastapi import FastAPI, APIRouter

router = APIRouter(prefix="")


def create_app():
    fast_app = FastAPI()
    fast_app.include_router(router)
    return fast_app


@router.get("/")
def read_root():
    return {"Hello": "World"}


if __name__ == '__main__':
    app = create_app()
    uvicorn.run(app=app)

Running the code will return a {"Hello": "World"} json when you visit the root endpoint / at http://127.0.0.1:8000. 😁

When you check the console window, the following log lines are printed:

INFO:     Started server process [10276]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:53491 - "GET / HTTP/1.1" 200 OK

Notice the Uvicorn log GET / HTTP/1.1″ 200 OK.

According to Uvicorn’s deployment docs we should run Uvicorn in a production settings with the following command: gunicorn -k uvicorn.workers.UvicornWorker main:create_app.

(venv2) ➜  FastAPILogging gunicorn -k uvicorn.workers.UvicornWorker main:create_app
[2021-05-17 22:10:44 +0300] [6250] [INFO] Starting gunicorn 20.1.0
[2021-05-17 22:10:44 +0300] [6250] [INFO] Listening at: http://127.0.0.1:8000 (6250)
[2021-05-17 22:10:44 +0300] [6250] [INFO] Using worker: uvicorn.workers.UvicornWorker
[2021-05-17 22:10:44 +0300] [6252] [INFO] Booting worker with pid: 6252
[2021-05-17 22:10:45 +0300] [6252] [WARNING] ASGI app factory detected. Using it, but please consider setting the --factory flag explicitly.
[2021-05-17 22:10:45 +0300] [6252] [INFO] Started server process [6252]
[2021-05-17 22:10:45 +0300] [6252] [INFO] Waiting for application startup.
[2021-05-17 22:10:45 +0300] [6252] [INFO] Application startup complete.

Now, if we visit the root endpoint, the console won’t print “GET / HTTP/1.1” 200 OK anymore/ 🤦‍♂️.

To fix it we need a custom UvicornWorker ⚙ and a logging configuration file 🗃.

Create a new file and name it logging.yaml, then paste the following contents in it:

version: 1
disable_existing_loggers: false

formatters:
standard:
format: "%(asctime)s - %(levelname)s - %(message)s"

handlers:
console:
class: logging.StreamHandler
formatter: standard
stream: ext://sys.stdout

loggers:
uvicorn:
error:
propagate: true

root:
level: INFO
handlers: [console]
propagate: no

This file will configure our root logger and our Uvicorn logger. To read more on the topic please see Python logging configuration.

Next, we will create a custom UvicornWorker class that will set log_config to the path of our logging.yaml file, to pass the logging configuration that we’ve just made to Uvicorn. 🦄

I added the following code in main.py:

class MyUvicornWorker(UvicornWorker):
    CONFIG_KWARGS = {
        "log_config": "/mnt/c/Users/denis/PycharmProjects/FastAPILogging/logging.yaml",
    }

▶ If we run the application with:

gunicorn -k main.MyUvicornWorker main:create_app

We should see the Uvicorn access logs printed in the console 🦄

(venv2) ➜  FastAPILogging gunicorn -k main.MyUvicornWorker main:create_app
[2021-05-17 22:31:28 +0300] [6278] [INFO] Starting gunicorn 20.1.0
[2021-05-17 22:31:28 +0300] [6278] [INFO] Listening at: http://127.0.0.1:8000 (6278)
[2021-05-17 22:31:28 +0300] [6278] [INFO] Using worker: main.MyUvicornWorker
[2021-05-17 22:31:28 +0300] [6280] [INFO] Booting worker with pid: 6280
2021-05-17 22:31:28,185 - WARNING - ASGI app factory detected. Using it, but please consider setting the --factory flag explicitly.
2021-05-17 22:31:28,185 - INFO - Started server process [6280]
2021-05-17 22:31:28,185 - INFO - Waiting for application startup.
2021-05-17 22:31:28,185 - INFO - Application startup complete.
2021-05-17 22:31:30,129 - INFO - 127.0.0.1:54004 - "GET / HTTP/1.1" 200

Thanks for reading! 📚

requirements.txt

click==7.1.2
fastapi==0.65.1
gunicorn==20.1.0
h11==0.12.0
httptools==0.2.0
pydantic==1.8.2
PyYAML==5.4.1
starlette==0.14.2
typing-extensions==3.10.0.0
uvicorn==0.13.4
uvloop==0.15.2

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