OpenTelemetry: implement a mapping from ZIO Metrics Summary to OTEL Histogram

[grouzen]

This functionality wasn't implemented in #801 as it is tricky to do.

As a reference you can look at the https://github.com/micrometer-metrics/micrometer library. It does exactly this for OTEL integration.

[IvanFinochenko]

Hi @grouzen
What do you think can we use OpenTelemetryMeterRegistry and DistributionSummary.Builder for this issue?

[IvanFinochenko]

I have researched some libraries and find this OpenTelemetryMeterRegistry
It has DistributionSummary, but methods for building OpenTelemetryMeterRegistry are not flexible.
I will try to create a PR with method builder taking OpenTelemetry Meter

[grouzen]

Hi @IvanFinochenko!
Sorry, don't have enough time at the moment to check this.
Regarding OpenTelemetryMeterRegistry - I don't think we need it since we maintain our own registry for our instruments. We just need to "copy" the way they map DistributedSummary to OTEL Histogram. The problem is the parts of the mapping algorithm are scattered all over the micrometer's codebase so it is tricky to understand it as a whole.

[grouzen]

@IvanFinochenko
We need to implement https://github.com/zio/zio-telemetry/blob/series/2.x/opentelemetry/src/main/scala/zio/telemetry/opentelemetry/metrics/internal/OtelMetricListener.scala#L40.
For this, we need to use registry.getHistogram and transform the payload of the ZIO Metrics Summary into OTEL Metrics Histogram. Hope it makes sense.

[grouzen]

@IvanFinochenko, we could do a pairing session in Discord, for example, if you want.

[IvanFinochenko]

@grouzen it is a good idea. I need a little more time to dive deeper under hood of micrometer and I'll write you.