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 `preferred_aggregation` parameter to `PrometheusMetricReader` to allow configuring default aggregation per instrument kind
+  ([#5117](https://github.com/open-telemetry/opentelemetry-python/pull/5117))
 - `opentelemetry-api`: Enforce W3C Baggage size limits on outbound propagation in `W3CBaggagePropagator.inject()`. Previously only inbound extraction enforced limits; now inject also caps entries at 180, individual pairs at 4096 bytes, and total header at 8192 bytes per the W3C Baggage spec. The extract path max_pairs limit now counts all size-valid entries rather than only successfully parsed ones.
   ([#5163](https://github.com/open-telemetry/opentelemetry-python/pull/5163))
 - `opentelemetry-sdk`: add `additional_properties` support to generated config models via custom `datamodel-codegen` template, enabling plugin/custom component names to flow through typed dataclasses

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 = "",
+        preferred_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=preferred_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,
@@ -47,6 +49,7 @@
 )
 
 
+# pylint: disable=too-many-public-methods
 class TestPrometheusMetricReader(TestCase):
     def setUp(self):
         self._mock_registry_register = Mock()
@@ -719,3 +722,30 @@ def test_multiple_data_points_with_different_label_sets(self):
                 """
             ),
         )
+
+    def test_preferred_aggregation(self):
+        """Test that preferred_aggregation parameter is passed to MetricReader."""
+        custom_aggregation = {
+            HistogramInstrument: ExplicitBucketHistogramAggregation(
+                boundaries=[1.0, 5.0, 10.0]
+            )
+        }
+        reader = PrometheusMetricReader(
+            preferred_aggregation=custom_aggregation
+        )
+        provider = MeterProvider(metric_readers=[reader])
+        meter = provider.get_meter("test")
+        histogram = meter.create_histogram("test_histogram")
+        histogram.record(5)
+        result = list(reader._collector.collect())
+        self.assertTrue(len(result) > 0)
+        prometheus_metric = result[1]
+        bucket_bounds = [
+            sample.labels["le"]
+            for sample in prometheus_metric.samples
+            if "le" in sample.labels
+        ]
+        self.assertIn("1.0", bucket_bounds)
+        self.assertIn("5.0", bucket_bounds)
+        self.assertIn("10.0", bucket_bounds)
+        reader.shutdown()