It’s a NIF! Oh no!

While people generally think NIFs are a bad idea, the overhead of this particular NIF is low. The C code that the NIF calls has been designed to be as fast as possible and to do as little as possible on the calling thread.

Internally, the AppSignal NIF works as follows: it fork/execs a separate agent process, to which the NIF sends its data (protobuf) over a unix socket. This agent process (which is a separate unix process!) then takes care of sending the data the the server periodically.

The C library that the NIF interfaces with, is specifically written with performance in mind and is very robust and battle tested; written in Rust and it is the same code that the Ruby AppSignal Gem uses, which is used in production in thousands of sites.

While doing native Elixir protobufs to communicate directly with this agent makes more sense from a BEAM standpoint, from a maintainability point the NIF choice is more logical because AppSignal is planning more language integrations in the future (PHP, Java) which all will use this same C library and agent process.