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Prometheus Client for Delphi

Delphi MVC Framework Prometheus Metrics middleware

Middleware for Prometheus Client to expose metrics using Delphi MVC framework

Prerequisites

This middleware is designed to work with Delphi MVC Framework.

If you use another library to build Web Server applications in Delphi (like Horse, 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/dmvc-prometheus-metrics

NOTE: if you download the package manually, also remember to get and configure the Prometheus Client for Delphi library.

Usage

To use this middleware, enable it calling MVCEngine.AddMiddleware() and passing the result of GetMetricsMiddleware(), a function available from the unit MVCFramework.Middleware.Metrics that creates an instance of the middleware object properly configured.

You can specify the path that exposes the metrics as a parameter or leave it blank to keep the default '/metrics' endpoint (which is the default path scraped by Prometheus server when collecting metric values):

  Engine.AddMiddleware(GetMetricsMiddleware('/metrics'));

You can also initialize a structure with custom configuration values to fine tune the features available "out of the box" inside the middleware (e.g. HTTP request duration metrics - thanks for Tuxino for the initial implementation!):

  begin var LConfig := TMVCMetricsMiddlewareConfig.Create('/metrics');
    LConfig.HttpRequestDurationEnabled := True;
    LConfig.HttpRequestDurationCollector := 'http_request_duration_seconds';
    FEngine.AddMiddleware(GetMetricsMiddleware(LConfig));
  end;

Then you can just declare the metrics you need registering them into the default collection registry. See the example below or the starter demo project for a tip to get started:

uses
  MVCFramework,
  MVCFramework.Middleware.Metrics,
  ...

begin
  Engine := TMVCEngine.Create(Self);

  Engine.AddMiddleware(GetMetricsMiddleware('/metrics'));

  TCounter
    .Create('http_requests_count', 'Received HTTP request count', ['path', 'status'])
    .Register();
end.

You can get a reference to your metrics inside controllers (or everywhere you need them).

uses
  MVCFramework,
  Prometheus.Collectors.Counter,
  Prometheus.Registry,
  ...

procedure TDemoController.HelloWorld;
begin
  TCollectorRegistry.DefaultRegistry
    .GetCollector<TCounter>('http_requests_count')
    .Labels([Context.Request.PathInfo, IntToStr(HTTP_STATUS.OK)])
    .Inc();

  Render('Done!');
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_request_duration_seconds Time taken to process request in seconds.
# TYPE http_request_duration_seconds histogram
http_request_duration_seconds_sum{path="/hello",status="200"} 11,1500155879185
http_request_duration_seconds_count{path="/hello",status="200"} 8
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.005"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.01"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.025"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.05"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.075"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.1"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.25"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.5"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="0.75"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="1"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="2.5"} 6
http_request_duration_seconds_bucket{path="/hello",status="200",le="5"} 7
http_request_duration_seconds_bucket{path="/hello",status="200",le="7.5"} 7
http_request_duration_seconds_bucket{path="/hello",status="200",le="10"} 8
http_request_duration_seconds_bucket{path="/hello",status="200",le="+Inf"} 8
http_request_duration_seconds_sum 11.1500155879185
http_request_duration_seconds_count 8
# HELP http_requests_count Received HTTP request count.
# TYPE http_requests_count counter
http_requests_count{path="/hello",status="200"} 8

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 and obviously Delphi MVC Framework.

Visit these web sites for getting started and read additional documentation about Prometheus and its client library for Delphi.

Happy coding! 🧑🏻‍💻