At the moment i'm trying to debug some issues with the server and try some solutions to see the impact. 

With little load i'm getting some percentage of "503 Server Unavaliable" errors from Kamailio. I made some testing without using database for anything but Dispatcher and Accounting and the performance got way better.

Right now, on this server, under as little as 20CPS Kamailio is returning "503" on 1-2% of all calls. However, my CPU and Memory look like this: 

%Cpu(s): 20.3 us, 6.1 sy, 0.0 ni, 73.3 id, 0.0 wa, 0.0 hi, 0.2 si, 0.2 st

Memory : 

              total used free shared buff/cache available

Mem: 1830 1172 382 109 274 375

Swap: 819 49 770

I have around 100 processes for Kamailio.

Cheers