I have a server with 20Cores / 40Threads.I used to have only one website app (rails / unicorn / nginx , 40 workers) on it and everything was working well. Recently I added a new website app (rails / unicorn / nginx, 2 workers) and since this, I have much less requests for my first website. htop stats seems to be normal.
How can I find out where is the bottle neck ? Maybe it is link with network, as my second apps is making external requests ? Or maybe IO access as my second apps is also reading and writting in the ssd disk..