Don't sleep on your Erlang literature: Learn You Some Erlang, Erlang in Anger, Design for Scalability with OTP. Also Little Elixir and OTP Guidebook is pretty short. I haven't read it yet, but Elixir in Action is supposed to be very good, too.

http://learnyousomeerlang.com/

https://www.erlang-in-anger.com/

https://smile.amazon.com/Designing-Scalability-Erlang-OTP-Fa...

https://www.manning.com/books/the-little-elixir-and-otp-guid...

https://www.manning.com/books/elixir-in-action