If your goal is file transfers only, then it seems like Erlang should contain mechanisms to handle that already. I believe Erlang implements an sftp server (ssh_sftp — OTP 29.0.2 (ssh 6.0.1)). I also see this article:
Which talks about building an ftp server on top of Ranch.
Accessing those things from Elixir to help with distributed coordination shouldn’t be too hard.
Honestly, if you find a faster option for templating at 100k req / sec I think we’d all like to know. 
It might even be worth contacting the folks over at Discord for some suggestions. Their engineering team has done a lot to push the limits of Elixir, open sourced and blogged about too.
We are currently looking into this Engine:
https://forum.elixirforum.com/t/fast-eex-iolist-option-for-eex-engine/16145/7
Looks promising thus far, I hope it can serve you well.
This is not anything new however, some folks at the community already gave it a shot, but I am not sure why this was not implemented (at the best of my knowledge, nothing was done with it).
That’s pushing the limits indeed. But IMO at this scale you’ll be much better off having 2-3 servers and putting a load balancer in front of them. Trying to squeeze every last drop of performance per watt is not using the dynamic languages like Erlang and Elixir to good use. They can crumble under such pressure.
If you really really want that server to remain singular then maybe it’s time to look into Rust or Go or OCaml.
At that scale on a single server then you are looking at pure socket performance, so C/C++ or Rust with specific libraries, or Nim (I’m still heavily impressed at its significantly loaded socket performance). I’d not recommend Go or OCaml, neither perform as well as C/C++/Rust/Nim when finely tuned (though they do well when not everything is finely tuned). You will be looking at memory pools, no-alloc structures, etc… etc… Honestly just adding more servers as better as redundency is always better for such things, at which point Elixir is just fine.
Still, hundreds of thousands per second is crazy high, I’m exceptionally curious what this is. ^.^
Well you have sockets, and something to compute an MD5 checksum - which is actually all you need.
Forget all the generic this and that and make a simple socket client and server (homework - find out the smallest socket client and server code)
Making a client/server over a socket is virtually the first thing I do in any language when learning - very instructive
Repeat in C, TCL, JS, Java, Ruby, Python, Perl, C#
Seriously, the round trip client → server → client with a check that you transfer all data and loose nothing is an essential programming technique - learn to do this first THEN add JSON/XML (whatever) on top.
Once you can get two programs in different languages communicating raw bytes over a socket then you can start having fun - Use the low level socket libraries and NOT fancy frameworks - this is the slow way to program - BUT in the long term the best way - understanding is the key to programming libraries which hide what you are really doing should only be used once you understand what’s really happening
Cheers
I will follow your “slow” way in Elixir to learn it with the help of your article “Why I often implement things from scratch”.
Thanks for your advice ! 
Very exciting debate on languages comparisons… Even if it drives me a bit far from my original concern ! 
Nevertheless, to fix some boundaries about my initial request:
