The low-hanging fruit when improving perceived performance is on the front-end, not the back-end, and certainly not the small overhead of the HTTP server.
processes = 2-4 * cpus
The GIL essentially serialises thread processing. This impacts throughput in threaded configurations.
Reverse proxy with nginx, etc. to decouple clients and app servers. Need to be able to kill backlogged requests when they aren’t needed; restarting some servers won’t clear a backlog.
Autoscaling configurations can cause load problems with fat applications; pre-configuring for required maximums.
Server monitoring tools largely treat web apps as a black box, they show the effects, not causes.
Apache modules are like “batteries included” for web-servers.