feat(exporter-metrics-otlp-http): respect OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION

[buzztaiki]

Which problem is this PR solving?

OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION was not respected by the OTLP metric exporters themselves. The env var was only handled by EnvironmentConfigFactory (the declarative config path used by startNodeSDK), which reads it and passes it explicitly as aggregationPreference to the constructor. Code that constructs the exporters without going through that path, including NodeSDK (class API) used by @opentelemetry/auto-instrumentations-node, silently ignored the env var.

Fixes #3920

Short description of the changes

Added chooseAggregationSelectorFromEnvironment() to OTLPMetricExporterBase, following the same pattern as the existing chooseTemporalitySelectorFromEnvironment() for OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE.

• When aggregationPreference is explicitly passed to the constructor, it takes priority (existing behavior unchanged).
• Otherwise, the env var is read: base2_exponential_bucket_histogram selects exponential histogram for histogram instruments; explicit_bucket_histogram (or unset) selects explicit bucket histogram; invalid values warn and fall back to DEFAULT.

Since OTLPMetricExporter in exporter-metrics-otlp-grpc and exporter-metrics-otlp-proto both extend OTLPMetricExporterBase, the fix applies to all three exporters.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Unit tests added to opentelemetry-exporter-metrics-otlp-http/test/node/OTLPMetricExporter.test.ts covering: default (unset), explicit_bucket_histogram, base2_exponential_bucket_histogram, case-insensitive matching, invalid value (warn + fallback), and constructor option taking priority over env var.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: buzztaiki / name: Taiki Sugawara (badc566)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.09%. Comparing base (27cd33a) to head (6724b1e).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6874   +/-   ##
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  Coverage   95.08%   95.09%           
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  Files         394      394           
  Lines       13997    14016   +19     
  Branches     3224     3231    +7     
=======================================
+ Hits        13309    13328   +19     
  Misses        688      688           

Files with missing lines	Coverage Δ
...er-metrics-otlp-http/src/OTLPMetricExporterBase.ts	91.46% <100.00%> (+2.57%)	⬆️

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[JacksonWeber]

Please don't forget to include a changelog.

[buzztaiki]

@JacksonWeber I've added change log entry for this PR.

[opentelemetry-pr-dashboard]

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Waiting on reviewers · refreshed 2026-07-29 01:44 UTC

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