[service] Add service::telemetry::metrics::views config key

[jade-guiton-dd]

Description

This PR adds a service::telemetry::metrics::views config key, which explicitly sets the list of metric views used for internal telemetry, mirroring meter_provider::views in the SDK config. This can be used to disable specific internal metrics, among other uses.

This key will cause an error if used alongside other features which would normally implicitly create views, such as:

• not setting service::telemetry::metrics::level to detailed;
• enabling the telemetry.disableHighCardinalityMetrics feature gate.

Further discussion needed

• A comment notes that the telemetry.disableHighCardinalityMetrics alpha gate "will be removed when the collector allows for view configuration". I think setting the gate as deprecated first would be the correct thing to do, but it means that users relying on it will see their Collectors crash on update. Is that okay?

• In the context of being able to enable/disable specific metrics, this key is only useful to disable metrics from an "all enabled" baseline. It cannot easily be used to customize the set of metrics emitted at level: normal, level: basic. Discussion is ongoing in Own-telemetry: Ability to enabled/disable individual metrics #10769 on how to handle that, but the solution will probably involve a new key, which should hopefully be backward-compatible with the user-visible changes in this PR.

Link to tracking issue

Updates #10769

Testing

None yet

Documentation

None yet, except the changelog

[codecov]

Codecov Report

Attention: Patch coverage is 65.21739% with 8 lines in your changes missing coverage. Please review.

Project coverage is 92.16%. Comparing base (dae5d19) to head (099fbd2).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
service/service.go	75.00%	4 Missing and 1 partial ⚠️
service/telemetry/config.go	0.00%	2 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (65.21%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12433      +/-   ##
==========================================
- Coverage   92.19%   92.16%   -0.04%     
==========================================
  Files         465      465              
  Lines       25285    25285              
==========================================
- Hits        23311    23303       -8     
- Misses       1575     1581       +6     
- Partials      399      401       +2     

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[mx-psi]

Can you increase the test coverage? Could you also add information about this (in a draft PR) to opentelemetry.io docs?

[jade-guiton-dd]

Regarding the lack of test coverage: it's almost entirely from the existing code for the feature gate that I just moved. I can try to add a new test for it; is there a way to set feature gates in tests?

[mx-psi]

Regarding the lack of test coverage: it's almost entirely from the existing code for the feature gate that I just moved. I can try to add a new test for it; is there a way to set feature gates in tests?

You can check the tests that are modified in #12377

[bogdandrutu]

Why this? I think we should allow views only if the level is not set.

[jade-guiton-dd]

The way we implement levels is by adding views that filter out unwanted metrics. But setting views explicitly completely replaces the default views (for now, we may decide to merge them later). There is discussion of this in the tracking issue, but I thought it would be confusing to add an empty views section and suddenly see more metrics than before. For that reason, I decided to only allows views with level: detailed, which enables all metrics and thus sets no views by default.

[jade-guiton-dd]

There was also the idea of adding a new level: custom value, so users explicitly declare their intent to bypass the level-based system and use more advanced view-based configuration, not sure what you think of it.