Prometheus exporter incorrectly adding units to metric name

[TylerHelmuth]

Description

I ran into an issue today bumping the operator to the latest collector version (v0.130.0) where the collector's metrics included the unit in the metric name unexpectedly. I expected the collector's emitted metric to be otelcol_exporter_sent_spans_total but saw otelcol_exporter_sent_spans__spans__total.

After investigating, I believe this is a result of #6839. For metrics the use the {} syntax, such as exporter_sent_spans the prometheus exporter is passing the suffix != "" check and proceeding to append the unit. The previous default behavior for a metric like {spans} was to not append the unit.

While I found this via the collector, I expect this issue would occur wherever the prometheus exporter is used.

Environment

• opentelemetry-go version: v1.37.0

Steps To Reproduce

Run a v0.130.0 collector with the following config:

receivers:
  otlp:
    protocols:
      http:
        endpoint: 0.0.0.0:4318
exporters:
  debug:
service:
  pipelines:
    traces:
      receivers: [otlp]
      processors: []
      exporters: [debug]
  telemetry:
    metrics:
      readers:
        - pull:
            exporter:
              prometheus:
                host: 0.0.0.0
                port: 8888

Sent a trace to http://localhost:4318.

Go to http://localhost:8888/metrics and see a metric named otelcol_exporter_sent_spans__spans__total

Expected behavior

A metric named otelcol_exporter_sent_spans_total

Work Around

If you manually set without_units: true the expected behavior occurs.

[andrzej-stencel]

I was able to confirm this. To make it easier to reproduce, here's how I sent a trace to the collector:

go install github.com/open-telemetry/opentelemetry-collector-contrib/cmd/telemetrygen@v0.130.0
telemetrygen traces --otlp-insecure --otlp-http

The without_units option must be added here: service::telemetry::metrics::readers[0]::pull::exporter::prometheus::without_units: true.

[dashpole]

We should migrate to the otlptranslator library to prevent issues like this in the future. I'll work on a PR and verify that it fixes this behavior

[povilasv]

i've tested with without_units: true and looks like it keeps the metric otelcol_exporter_sent_spans_total metric from becoming otelcol_exporter_sent_spans__spans__total

but then breaks many others metrics, as it will remove units:

otelcol_process_memory_rss_bytes => otelcol_process_memory_rss
otelcol_process_uptime_seconds => otelcol_process_uptime
otelcol_otelsvc_k8s_pod_added_ratio => otelcol_otelsvc_k8s_pod_added

So it's also not an ideal fix 😕 And rather unclear what is better to use without_units: true or not.

[mx-psi]

I think this should bump the priority of fixing this issue (or of finding an alternative workaround)