Would need more information. I’ve seiged my server with over a 30k requests per second on 2-cores without an incorrect result (and after that it just slows down a lot more but still no incorrect, dropped, or invalid responses).
If it’s a 504 Gateway Time-out that sounds like there is a front-loader/gateway in front of Elixir and it is what’s getting overwhelmed (perhaps it has only a single connection open to the backend server?).
What is the gateway program, what defines ‘high load’, what is the gateway’s configuration for the reverse proxy, what are the hardware specs, etc… etc… 
