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Why a NIF?

The AppSignal for Elixir integration relies on a NIF that calls out to a library to do the heavy lifting, written in Rust. Its job is to receive data from the Elixir side, normalize it and write it to a separate agent process over a Unix socket. The agent then sends the data to periodically for further processing.

While using NIF's has inherent risks, using one in this case has several advantages:

  1. Overhead is very low. The functions in the NIF do nothing more than receive data and send it to a worker thread, so that the C function can return immediately. It's designed to be as fast as possible while having very little impact on the calling thread, and generate minimal garbage collection load.
  2. It allows the use of the same library and agent used by AppSignal for Ruby, which runs on thousands of production servers all over the world. It's battle tested technology, processing a combined 1 billion requests per day (November 2016).
  3. The library and agent are written in Rust, and its primary design considerations were (and remain) robustness and performance.

Internally, the AppSignal NIF works as follows: it fork/execs a separate agent process, to which a worker thread in the NIF sends its data over a Unix socket. All I/O and processing in the NIF is asynchronous, so calls to its functions will never hold up the scheduler. In the very unlikely event that something in the extension panics, the extension disables itself without bringing down the host process.

While doing native Elixir protobufs to communicate directly with the agent makes more sense from a BEAM standpoint, using a NIF enables the use of a single library. This decreases potential issues because of the volume of testing and fine-tuning that has already happened. By focusing on a single code base, AppSignal can guarantee the highest quality for all of its customers across all supported languages.

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