Horse Prometheus Metrics middleware

Middleware for Prometheus Client to expose metrics using Horse Web framework

Prerequisites

This middleware is designed to work with Horse Web framework.

If you use another library to build Web Server applications in Delphi (like DMVC, MARS, Web Broker, etc.), checkout if there are samples that can help you out bootstrapping your application or ready-to-use middlewares for your framework.

How to install

To install this middleware in your project, download source code from GitHub and set the library path as usual, or launch this command to get all the needed packages using boss package manager:

$ boss install marcobreveglieri/horse-prometheus-metrics

NOTE: if you download the package manually, also remember to get and configure the Prometheus Client for Delphi library. This middleware works only with Horse Web framework!

Usage

To use this middleware, enable it calling THorse.Use() passing the appropriate callback (see below) specifing the '/metrics' endpoint (which is the default path scraped by Prometheus server); then, just declare the metrics you need registering them into the default collection registry.

uses Horse, Horse.Prometheus.Metrics,

begin
  THorse.Use('/metrics', PrometheusMetrics());

  TCounter
    .Create('http_requests_handled', 'Count all HTTP handled requests', ['path', 'status'])
    .Register();

  THorse.Get('/ping',
    procedure(Req: THorseRequest; Res: THorseResponse)
    begin
      TCollectorRegistry.DefaultRegistry
        .GetCollector<TCounter>('http_requests_handled')
        .Labels([Req.PathInfo, IntToStr(Res.Status)])
      .Inc();
      Res.Send('pong');
    end);

  THorse.Listen(9000);
end.

Test it!

By calling the route /metrics (or any different path specified when enabling the middleware) you will get a plain text response that includes all the current metric values collected from the default collector registry.

# HELP http_requests_handled Count all HTTP handled requests.
# TYPE http_requests_handled counter
http_requests_handled{path="/ping",status="200"} 4
http_requests_handled{path="/secret",status="401"} 2

Additional info

If you want to know more about Prometheus, visit the official homepage and download the right version of this tool.

This middleware also requires to install the Prometheus Client for Delphi library. Visit these web sites for getting started and read additional documentation about Prometheus and its client library for Delphi.

Happy coding! 🧑🏻‍💻