How to use WEB_CONCURRENCY with the prefect server

[balazs-tothfalussy]

Hi, I am wondering how to properly use uvicorn's workers with the WEB_CONCURRENCY environment variable together with the prefect server:

❯ WEB_CONCURRENCY=8 prefect server start
...
WARNING:  You must pass the application as an import string to enable 'reload' or 'workers'.
Server stopped!

This affects the foreground server mode, while starting in the background works, but affects the official helm chart that we try to use with Kubernetes as I think that also uses the foreground version. I am using version 3.4.17.

Foreground runner uses a python object: https://github.com/PrefectHQ/prefect/blob/main/src/prefect/cli/server.py#L478
Bacground runner a string param: https://github.com/PrefectHQ/prefect/blob/main/src/prefect/cli/server.py#L430

Thanks!

[balazs-tothfalussy]

Oh, I see this is basically fixed in 3.20 and https://github.com/PrefectHQ/prefect/pull/18876/files#diff-67cb09cb51040314850d151cd3c20b33ef420dcbce7f07dd186b1911812717e6 by introducing the workers parameter.