how many uvicorn workers do I have to have in production?

Question

My Environment

• FastAPI
• Gunicorn & Uvicorn Worker
• AWS EC2 c5.2xlarge (8 vCPU)

Document

https://fastapi.tiangolo.com/deployment/server-workers/

Question

Currently I'm using 24 Uvicorn workers in production server. (c5.2xlarge)

gunicorn main:app --workers 24 --worker-class uvicorn.workers.UvicornWorker --bind 0.0.0.0:80

I've learn that one process runs on one core. Therefore If i have 8 processes, I can make use of whole cores (c5.2xlarge's vCpu == 8)

I'm curious that in this situation, Is there any performance benefit if I got more processes than 8?

Answer 1

Number of recommended workers is 2 x number_of_cores +1

You can more about it in the official documentation.

In your case with 8 CPU cores, you should be using 17 worker threads.

Additional thoughts on async systems:

The two times core is not a scientific figure as says in the article. But the idea is that one thread can do I/O and another CPU processing at the same time. This makes maximum use of simultaneous threads. Even with async systems, conceptually this works and should give you maximum efficiency.