I've made an additional investigation and found out that for some reason Fusionauth instances deployed in my k8s cluster don't utilize all CPUs available on the nodes. There are 6 nodes with 12 CPUs each, but a single Fusionauth instance hardly ever utilized even 1 CPU.

I've tried to scale horizontally, deploying 50, 60, 75 and more Fusionauth's instances and got much better result during my load testing, up to 250 logins per second (each login - two requests - /oauth2/authorize and /oauth2/token).

I wonder why this could happen and and if there are there any settings for Fusionath or Java or k8s that could help to solve the issue?