Tracking issue: SDK Prometheus exporter spec-compliance

[dashpole]

I did a mini-audit of the current state of prometheus exporters in the OTel ecosystem a little while back. I'm leaving a tracking issue here to be able to easily see how those issues are progressing.

Go is compliant

Java:

• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-java#5014
• Prometheus exporter handles delta metrics differently from the current spec opentelemetry-java#5015

Python:

• Prometheus exporter should convert non-monotonic sums to gauges opentelemetry-python#3071
• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-python#3072
• Prometheus exporter emits target_info for Resource opentelemetry-python#3073

JS:

• Consider following OpenMetrics guidance on timestamps opentelemetry-js#3463
• Prometheus exporter: replace repeated _ with a single _ opentelemetry-js#3464
• Prometheus exporter should use NaN instead of Nan opentelemetry-js#3465
• Prometheus exporter: Add unit to metric names, and convert unit to words opentelemetry-js#3466
• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-js#3467

C++:

• Prometheus exporter: Add unit to metric names, and convert unit to words opentelemetry-cpp#1840
• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-cpp#1841
• Prometheus exporter emits target_info metric using Resource opentelemetry-cpp#1842
• Prometheus exporter sanitizes invalid name characters opentelemetry-cpp#1843

.NET:

• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-dotnet#3972
• Prometheus exporter: counters should have _total suffix opentelemetry-dotnet#3973
• Prometheus exporter: Non-monotonic sum should be converted to a prometheus gauge opentelemetry-dotnet#3974
• Prometheus exporter: unit, name, label sanitization improvements opentelemetry-dotnet#3975

Rust:

• Prometheus Exporter: Counters should have _total suffix opentelemetry-rust#926
• Prometheus exporter: Unit in metric names opentelemetry-rust#927
• Prometheus exporter: sanitization tweaks opentelemetry-rust#928
• Prometheus exporter: Use OTel Resource for target_info opentelemetry-rust#929
• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-rust#930

Swift:

• Prometheus exporter: gauges should be exported as prometheus gauges opentelemetry-swift#353
• Prometheus exporter: Counters must have _total suffix opentelemetry-swift#354
• Prometheus exporter: histogram bucket series must have _bucket suffix opentelemetry-swift#355
• Prometheus exporter: Omit timestamps from metrics opentelemetry-swift#356
• Prometheus exporter: Histograms +Inf bucket should be equal to count opentelemetry-swift#357
• Prometheus exporter: Non-monotonic sums should be converted to gauges opentelemetry-swift#358
• Prometheus exporter: Unit as suffix for metric name opentelemetry-swift#359
• Prometheus exporter: emit target_info metric using Resource opentelemetry-swift#360
• Prometheus exporter handles instrumentation scope and prevents collisions opentelemetry-swift#361

@open-telemetry/wg-prometheus

[marcalff]

@dashpole

Please also track the prometheus exporters located in the opentelemetry-collector.

• https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/exporter/prometheusexporter
• https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/exporter/prometheusremotewriteexporter

Use case:

• an application is instrumented to emit metrics
• exports metrics using the OTLP exporter (not Prometheus)
• to an opentelemetry-collector
• which forwards the data to prometheus

[dashpole]

Related OpenTelemetry Collector issues:

• prometheusremotewrite: support for converting OTLP exponential histogram to Prometheus Native Histograms opentelemetry-collector-contrib#16207
• [prometheusreceiver] Convert Info and StateSet metrics to non-monotonic sums opentelemetry-collector-contrib#8516
• [prometheusexporter] Add job and instance labels to match federated prometheus opentelemetry-collector-contrib#8355
• [prometheusreceiver] Support exemplars from Prometheus opentelemetry-collector-contrib#8353
• [prometheusremotewriteexporter] TraceID and SpanID must be added as exemplar attributes. opentelemetry-collector-contrib#8351
• [prometheus components] Translate the "target" info metric to/from resource attributes opentelemetry-collector-contrib#8265
• [prometheusexporter] / [prometheusremotewriteexporter] Support for exemplars opentelemetry-collector-contrib#5192
• [prometheusreceiver/prometheusexporter] Handle units in prometheus metric names opentelemetry-collector-contrib#8950
• Should prometheus metric name normalization be exposed as a configuration option? opentelemetry-collector-contrib#21743

[gouthamve]

Go has a couple of issues: open-telemetry/opentelemetry-go#4371 and open-telemetry/opentelemetry-go#4372