Prometheus Histogram Metrics Label “le” are converted from Double to Int

[SkylarLNH1029]

Problem:
I recently switched from grafana agent to otel collector to scrape Prometheus metrics.

Inside the Orel collector, I have a Prometheus receiver and a Prometheus remote write exporter.

After this switch, I noticed the values of my Prometheus histogram bucket metric label “le” changed from for example “900.0” to “900”.

My questions:

1. Does otel directly forward the original Prometheus metrics from receiver to exporter since they don’t require any format change? Or does otel convert Prometheus to otlp when receiving and then convert from otlp to Prometheus when exporting? If that’s the case, would there be any incompatibility in the process?
2. What caused my labels changing from “900.0” to “900”. Does otel convert double/float to int? Or is there some configuration I need to set?

[github-actions]

Pinging code owners for receiver/prometheus: @Aneurysm9 @dashpole. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[dashpole]

Interesting. The internal representation of histogram boundaries in the collector is a Float64 Slice. So it can't be converting to an int.

This sounds like it might be an issue with the prometheusremotewrite exporter's encoding of the float boundaries. This is what it does today:

opentelemetry-collector-contrib/pkg/translator/prometheusremotewrite/helper.go

Line 255 in fa5e8f1

boundStr := strconv.FormatFloat(bound, 'f', -1, 64)

The prometheus Go client does this to encode floats in the exposition format: https://github.com/prometheus/common/blob/d726751c69dc327617a6b294f0f1e8d448291d15/expfmt/text_create.go#L480

*bp = strconv.AppendFloat((*bp)[:0], f, 'g', -1, 64)

'g' and 'f' don't seem to make a difference, though: https://go.dev/play/p/KDpgzrHq42O

[dashpole]

Based on the text format example: https://github.com/prometheus/docs/blob/main/content/docs/instrumenting/exposition_formats.md#text-format-example, the correct encoding of the float 1.0 is actually just 1 for the le label. I'm inclined to conclude that the current behavior is correct.

[github-actions]

Pinging code owners for pkg/translator/prometheusremotewrite: @Aneurysm9. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

Pinging code owners for exporter/prometheusremotewrite: @Aneurysm9 @rapphil. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• exporter/prometheusremotewrite: @Aneurysm9 @rapphil
• pkg/translator/prometheusremotewrite: @Aneurysm9

See Adding Labels via Comments if you do not have permissions to add labels yourself.