feat(exporter/prometheus): add default_aggregation parameter to PrometheusMetricReader

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- `opentelemetry-exporter-prometheus`: Add `default_aggregation` parameter to `PrometheusMetricReader` to allow configuring default aggregation per instrument kind
+  ([#5109](https://github.com/open-telemetry/opentelemetry-python/issues/5109))
 - `opentelemetry-sdk`: fix YAML structure injection via environment variable substitution in declarative file configuration; values containing newlines are now emitted as quoted YAML scalars per spec requirement
   ([#5091](https://github.com/open-telemetry/opentelemetry-python/pull/5091))
 - `opentelemetry-sdk`: Add `create_logger_provider`/`configure_logger_provider` to declarative file configuration, enabling LoggerProvider instantiation from config files without reading env vars

exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

@@ -105,6 +105,9 @@
     MetricsData,
     Sum,
 )
+from opentelemetry.sdk.metrics.view import (
+    Aggregation,
+)
 from opentelemetry.semconv._incubating.attributes.otel_attributes import (
     OtelComponentTypeValues,
 )
@@ -135,7 +138,10 @@ class PrometheusMetricReader(MetricReader):
     """Prometheus metric exporter for OpenTelemetry."""
 
     def __init__(
-        self, disable_target_info: bool = False, prefix: str = ""
+        self,
+        disable_target_info: bool = False,
+        prefix: str = "",
+        default_aggregation: dict[type, Aggregation] | None = None,
     ) -> None:
         super().__init__(
             preferred_temporality={
@@ -146,6 +152,7 @@ def __init__(
                 ObservableUpDownCounter: AggregationTemporality.CUMULATIVE,
                 ObservableGauge: AggregationTemporality.CUMULATIVE,
             },
+            preferred_aggregation=default_aggregation,
             otel_component_type=OtelComponentTypeValues.PROMETHEUS_HTTP_TEXT_METRIC_EXPORTER,
         )
         self._collector = _CustomCollector(

exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py

@@ -28,6 +28,7 @@
     _CustomCollector,
 )
 from opentelemetry.metrics import NoOpMeterProvider
+from opentelemetry.sdk.metrics import Histogram as HistogramInstrument
 from opentelemetry.sdk.metrics import MeterProvider
 from opentelemetry.sdk.metrics.export import (
     AggregationTemporality,
@@ -38,6 +39,7 @@
     ResourceMetrics,
     ScopeMetrics,
 )
+from opentelemetry.sdk.metrics.view import ExplicitBucketHistogramAggregation
 from opentelemetry.sdk.resources import Resource
 from opentelemetry.test.metrictestutil import (
     _generate_gauge,
@@ -719,3 +721,21 @@ def test_multiple_data_points_with_different_label_sets(self):
                 """
             ),
         )
+
+        def test_default_aggregation(self):
+            """Test that default_aggregation parameter is passed to MetricReader."""
+            custom_aggregation = {
+                HistogramInstrument: ExplicitBucketHistogramAggregation(
+                    boundaries=[1.0, 5.0, 10.0]
+                )
+            }
+            reader = PrometheusMetricReader(
+                default_aggregation=custom_aggregation
+            )
+            self.assertEqual(
+                reader._instrument_class_aggregation[
+                    HistogramInstrument
+                ].__class__,
+                ExplicitBucketHistogramAggregation,
+            )
+            reader.shutdown()