Prometheus exporter: Add default aggregation config option

.changelog/5249.added

@@ -0,0 +1 @@
+`opentelemetry-exporter-prometheus`: add `default_aggregation` to `PrometheusMetricReader`

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

@@ -94,6 +94,7 @@
     MetricsData,
     Sum,
 )
+from opentelemetry.sdk.metrics.view import Aggregation
 from opentelemetry.semconv._incubating.attributes.otel_attributes import (
     OtelComponentTypeValues,
 )
@@ -129,6 +130,7 @@ def __init__(
         prefix: str = "",
         *,
         registry: CollectorRegistry = REGISTRY,
+        default_aggregation: dict[type, Aggregation] | None = None,
     ) -> None:
         super().__init__(
             preferred_temporality={
@@ -139,6 +141,7 @@ 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

@@ -17,7 +17,7 @@
     _CustomCollector,
 )
 from opentelemetry.metrics import NoOpMeterProvider
-from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.metrics import Counter, MeterProvider
 from opentelemetry.sdk.metrics.export import (
     AggregationTemporality,
     Histogram,
@@ -27,6 +27,7 @@
     ResourceMetrics,
     ScopeMetrics,
 )
+from opentelemetry.sdk.metrics.view import DropAggregation
 from opentelemetry.sdk.resources import Resource
 from opentelemetry.test.metrictestutil import (
     _generate_gauge,
@@ -89,6 +90,25 @@ def test_constructor(self):
             _ = PrometheusMetricReader()
             self.assertTrue(self._mock_registry_register.called)
 
+    def test_constructor_default_aggregation(self):
+        custom_registry = CollectorRegistry()
+        metric_reader = PrometheusMetricReader(
+            disable_target_info=True,
+            registry=custom_registry,
+            default_aggregation={Counter: DropAggregation()},
+        )
+        provider = MeterProvider(metric_readers=[metric_reader])
+
+        meter = provider.get_meter("getting-started", "0.1.2")
+        counter = meter.create_counter("counter")
+        counter.add(1)
+
+        self.assertEqual(
+            generate_latest(custom_registry).decode("utf-8"),
+            "", # DropAggregation drops all measurements, so no metrics are exported
+        )
+        provider.shutdown()
+
     def test_shutdown(self):
         with patch(
             "prometheus_client.core.REGISTRY.unregister"