How to add custom collector?

[FixRM]

Hello, I'm trying to export existing monitoring statistics in Prometheus format using this library. I tried to create custom ICollector implementation and add it on startup like this: Metrics.DefaultCollectorRegistry.Add(new MyCollector());. The problem is that I got internal errors while writing to IMetricsWriter as it is not clear what methods should I call and in what order. Can you please point me to documentation or existing sample? I tried to figure that out from the Gauge sources, but It seems to be too complicated for me)

p.s. May be there is a better option?

[phnx47]

@FixRM Hi, did you look standard collectors, example GCCollectionCountCollector?

[FixRM]

Hi @phnx47! Thank you, it works! Can you please explain me the purpose of each entity in hierarchy Metric -> Sample -> Label. For instance, it is not clear what is string value parameter of WriteLabel.

[phnx47]

Both of them are fine. With low-level ICollector you work with IMetricsWriter, with high-level you can use Gauge or Untyped metrics, like this:

var gauge = metricFactory.CreateGauge("gauge", "help text");
gauge.Set(5);

[FixRM]

Ok, thanks. That is entry point for high level API in my case? How can I understand that it's time to update my metrics?

[phnx47]

@FixRM It depends what you need, in your case is HangFire, check with Hangfire.Prometheus how they update.

[FixRM]

It is library what I ported to your framework ) It use Metrics.DefaultRegistry.AddBeforeCollectCallback to add gauge in the way you suggested, but this method is not available in your port.

[phnx47]

I checked code in Hangfire.Prometheus

With ICollector - metrics will be collected with every request from Promethues. Similar Hangfire.Prometheus.
With Gauge - you need periodically set updated values yourself. If you have any trigger from Hangfire, you can use it or some Backgroud Job.