Can't Add Collectors During Setup

[Spinkelben]

With the change to use DI for injecting the ICollectorRegistry the CollectorRegistryInstance property of PrometheusOptions becomes useless. We used to configure our metrics like this.

app.UsePrometheusServer(prometheusOptions =>
{
    prometheusOptions.CollectorRegistryInstance.Add(new MySystemMetricCollector());
});

This no longer works. The property is null. If I create a new CollectorRegistry in this method it is ignored. So I would suggest you set it before invoking the setup function.

[Spinkelben]

Hmm, maybe I was too fast. I didn't fully understand the meaning of the ??= operator of this code:

options.CollectorRegistryInstance
                    ??= (ICollectorRegistry)app.ApplicationServices.GetService(typeof(ICollectorRegistry))
                    ?? Metrics.DefaultCollectorRegistry;

[Spinkelben]

Ah, I found the real issue. I guess I was partially correct. We use DI to inject a IMetricFactory. That includes a ICollectorRegistry instance. Unless we use the same ICollectorRegistry instance in the setup method, it has no effect. This code would fix it:

app.UsePrometheusServer(prometheusOptions =>
{
    prometheusOptions.CollectorRegistryInstance = app.ApplicationServices.GetService<ICollectorRegistry>();
    prometheusOptions.CollectorRegistryInstance.Add(new MySystemMetricCollector());
});

However it is a bit stupid. It would be better, if we got the ICollectorRegistry instance from the PrometheusOptions object, when it is already registered in the DI container.

[sanych-sun]

Hi @Spinkelben!

Sorry for the late response. If you are using DI integration library - the answer is simple: just remove the CollectorRegistryInstance property from options and it will be resolved from DI.

Currently we are using the following order:

1. use collector registry from options
2. try to resolve it from DI
3. use static instance (as a fallback for backward compatibility).

So returning to the original issue: if you trying to register additional collectors - it would be better to resolve the ICollectorRegistry from DI somewhere on your side and add the collector to it. Or you can create instance of CollectorRegistry on your side, add your collector, and then use overloaded method to register MetricFactory by providing registry instance.

However you probably right - it will be better try to resolve the actual collector registry before calling configuration method.