exporter/prometheus: why is add_metric_suffixes enabled by default?

[wbollock]

Component(s)

exporter/prometheus

Describe the issue you're reporting

I was surprised to see that add_metric_suffixes is enabled by default. It is an opinionated feature flag that modifies metrics in a way some operators may not expect. It can be difficult to track down why metrics are not available anymore just to find that opentelemetry-collector-contrib is automatically changing their series names.

I propose the setting is turned off by default instead as the default behavior of the Prometheus exporter should be to simply relay the metrics it is told to expose rather than conform them to specific standards.

From what I can tell it is set to true to preserve even older behavior: 2bc9904

[github-actions]

Pinging code owners:

• exporter/prometheus: @Aneurysm9 @dashpole @ArthurSens

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[dashpole]

This has been a topic of much discussion. We even ran a community survey to better understand sentiment: https://opentelemetry.io/blog/2024/prometheus-compatibility-survey/, which showed that opinions on the topic are very split.

For suffixes in particular, there are a few challenges:

• OpenMetrics requires unit suffixes on the metric name and _total suffixes on counter timeseries, which i'm hoping to change in a future version of OpenMetrics.
• Units are identifying in OpenTelemetry, but not in Prometheus. I'm hoping to change that in Prometheus Proposal: Add type and unit metadata labels prometheus/proposals#39 to prevent collisions between metrics with the same name but different unit.

I agree we should change the default to preserve the original name, but it will take some time to get there.