Meter Tags and Prometheus HttpListener

[ProbablePrime]

Hello,

I'm having difficult understanding, the use of Tags and the resultant Prometheus output, from a System.Diagnostics.Metrics.Meter vs a System.Diagnostics.Metrics.Instrument<T>'s Add/Set Method.

The documentation for Metric Enrichment mentions:

Additional tags provided at meter creation time. For example, the Meter(name, version, tags, scope) overload.

But these do not appear to be working, when tags from Meter creation are specified they are not present in the Prometheus Output.

I started looking over on Stack Overflow, and found this question. Which is identical to my issue.

But I wanted to make it even easier to help the community here see what's going on.

So on a fork of opentelemetry-dotnet, I have edited a test to show the issue. You can find the whole commit.

But, to help further:

1. Here's where I have added Meter scoped tags
2. Here's where I edited the test output, to include the new meter tags

These changes result in a failing test as the Meter based tags are not present, but based on the documentation, I feel this should be working.

It looks like only tags that are sent with a metric's value (via Set, Add, Record etc) are propagated.

However, questions on this area seem to come up somewhat frequently so I'm a little confused. For example there's:

• Instrument tags not attached #5478
• Counter tags not attached #5313
• Add support for instrumentation scope attributes (Meter tags) #5089 - This one introduced the test I modified.

As such I am not sure:

• If this is a new issue/bug that needs to be reported as an Issue?
• If this is covered elsewhere such as the items I linked
• If this is not possible due to another factor.

Could anyone provide some guidance?

[ProbablePrime]

This also affects "Observable" Instruments.

Capacity = Meter.CreateObservableGauge<int>($"{MetricPrefix}.capacity", () => capacity, "XXX", "XXX", Tags);

Tags created in this way also do not show up.

[cijothomas]

https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/src/OpenTelemetry.Exporter.Prometheus.AspNetCore/CHANGELOG.md#180-beta1

Prometheus supports instrumentation scope (Meter tags), only when OpenMetrics format is used. Is that your case?

[ProbablePrime]

Thank you!, I was not using the "application/openmetrics-text", content header in my target application.

However, even when swapping to it, Meter Tags still do not show up.

I updated the test case fixture on my fork, to only have the meter tags in the requestOpenMetrics version of the fixture: ProbablePrime@69394b5

This test still fails:

[cijothomas]

Got it. It looks like a bug in Prometheus exporter. It is only exposing Meter name for the scope, not the version, not the tags! Could you report it as a bug?

[ProbablePrime]

I will get to this as soon as I can. I'll see about making a minimum reproduction to help as well!

[cijothomas]

It is well understood, so no need to work on a repro.

@robertcoltheart Would you have some bandwidth to make this feature?

[robertcoltheart]

Sure, will take a look this week 👍

[ProbablePrime]

Ok I'll stand up a bug today!

Thank you for this!