Of course there is nothing requiring you to use Phoenix You have several options in the community, such as dropping down to plain Plug (which phoenix is built on), or using another Elixir webserver/library combo like Ace/Raxx, or even using Cowboy (an Erlang web server) from Elixir. Using Phoenix will not impose measurable overhead performance wise, and what you may lose by forgoing it depends on what exactly you’re building– which we have light details on. I will say Phoenix is great for API servers and it’s probably your most mature option. The SQLServer integration will be handled the same way regardless of your choice web wise. Maybe prototype out a couple options and see what fits best?

I guess you’d need to clarify what you mean by “super fast”, “forex api server”, and how you are planning to use sqlserver in this setup.

Since phoenix is mostly geared towards web dev, it’s TCP-based. For “super fast” you might want to go with UDP. Although I’m not sure what “forex api server” here means, do you plan to make API requests to some other exchanges, and aggregate the results? And you might want to pick an in-memory database instead of a disk-based one.

I would revisit whether you even want to use UDP - there are plenty of scenarios where TCP is much faster than UDP and generally it’s the sane choice for building an API if you’re unsure about which one will fit your needs.