Much have been said about you should stick with a pure Elixir approach, then only move on to Rust NIF when there is significant benefit in doing so. I want to point out the CGI style System.cmd interface is most likely not what you want, should you decide that neither pure Elixir nor Rust NIF is good enough for you.

If you must use an external process, then the only valid reason is that you need to keep significant state in that external process. The best way to communicate with a stateful external process is via a port. Rust offers an excellent async library, Tokio, to make that happen. You would need to write a couple hundred lines of Rust code to wrap the Rust library though.

Are you willing to sacrifice all the benefits of elixir for some performance? If yes then go with 2.

Yes. With external programs you have to marshall communication in both directions. Staying with elixir means you don’t need to do that.

Not sure you can have something be faster when it hits the network. The CPU is just waiting for a response.

And in your case you don’t even have a Rust library to call in-process, you have an external tool.

I’d say stick to Elixir unless the Rust tool is bringing critically important benefits.

I am prone to being preachy and absolutist sometimes so maybe I am not the best person to give an answer… but I am leaning to “yes”.

To me calling something in-process has less things that can go wrong. Though seriously, tools that are well-behaved are probably just as safe. (“Well-behaved” in this instance means “they respect shell conventions when having to stream data in/out from/to stdin/stdout”).

Of course I’d also seriously consider just doing the whole thing in Elixir if I can get away with it. As mentioned above, disk or network I/O are 1000x more time-expensive compared to CPU-intensive tasks so who cares if your code that will need 350ms to get back an answer from an external server is written in Rust, Go, Haskell or even Ada or Brainfuck?

Even more supporting my conclusion then. I/O-bound tasks can be written in whatever. You don’t need Rust for that; Rust is for when you need every last bit of performance and minimal memory pressure.