There have also been several threads on elixirforum about performance in benchmarks. Some of them might be relevant to you.
which_is_the_fastest benchmark though had a strange benchmarking tool, so those results might be discarded.
cowboy1-and-cowboy2 is also somewhat controversial since in a blog post by @potatosalad Load Testing cowboy 2.0.0-rc.1 · potatosalad cowboy2 was much faster than cowboy1 and in my tests it was the opposite (different benchmarking tools).
Some general notes:
Make sure to remove unecessary plugs from your endpoint.
Make sure you are comparing apples with apples. For example, if one is logging and the other isn’t, that’s going to be a huge difference in performance.
Make sure to set max_keepalive otherwise connections will be recycled over and over again
A larger connection pool often implies worst performance, because there is less resource sharing
But in general, if you are getting 408ms for such a simple page, @OvermindDL1 is right: there is something absurdly wrong.
Thanks for all your suggestions !
408ms is an average based on the wrk load test above. I’m going to try to improve the results, I think I’ll get better load times by tuning the EVM/elixir and FreeBSD.
Well if someone could perform the same tests and confirm the cowboy/fasthttp load time ratio … Should not take more than 15 minutes 
Regarding the max_keepalive: before increasing it I want to understand how connection pooling works exactly in cowboy. And assess if this server is subject to Slow HTTP Dos Attacks such as described here:
In one of the posts above I saw someone setting it to 5_000_000 … wow 
And assess if this server is subject to Slow HTTP Dos Attacks such as described here:
Still, I usually put haproxy in front of erlang webservers (I usually use elli).
Cowboy’s max_keepalive is not a timeout, it’s the maximum number of HTTP requests that can be done reusing the same connection. It has a separate timeout and maximum number of connections.
https://github.com/ninenines/cowboy/commit/a013becc66b50db038c1f7f3539040b4482bba18
https://github.com/ninenines/cowboy/commit/5d698250b228229001ca9966a390bf1545fcd0b0
So I’ve re-run several tests setting max_keepalive to 5_000_000.
With:
wrk -t12 -c12 -d1s -T10s http://.../fortune
I get an average latency of 8.3 ms and max latency of 100ms.
With (same as my initial tests):
wrk -tc -c12000 -d60s -T10s http://.../fortune
I get an average latency of 404ms ms and max latency of 707ms.
Max latency is much better ! 700ms instead of 8000ms
I’ve also tried to lower db pool size to 20, avg latency decreased to 390ms.
Though the average latency remains @400ms.
Thanks for links regarding the slow attacks, I’ll have to read all of this. Even if Cowboy servers are not in front I prefer to be very cautious when dealing with such config params. Might as well induce resource exhaustion. I’ll run some tests when I have time.
I’m going deeper underground