Are there any tools or ways to determine the bottleneck in the architecture (php apache mysql)?

Question

LAMP

Hello.
Maybe someone already had experience with the definition of a bottleneck in a server.
The case is next.
There is a server: 12-core percent, (2.6Ghz per core). 24 GB RAM, 200 GB SSD broom.
I have an application written in Symfony. The page is given in 250ms, which is not bad in principle, and the code itself works out in 150ms. I would like to know what it will be clamped at high loads (lack of memory for MySQL, lack of processor for PHP, or lack of I / O for content).
For each of these options, there are decisions worth making. I just want to know where to optimize better.
Possible solutions:
for a web server - splitting into several servers with a balancer.
for MySQL - replication.
for content - CDN.
Thanks for the advice!
PS Application architecture - monolithic.

Answer 1

Set up logging
Turn on atop iotop Load
Look
Look at the
logs

Answer 2

so can load testing do? It is clear that this will not repeat the real work directly at 100% - but it will obviously be closer to reality than theoretical calculations.