adds config to enable default exponential histogram

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/PrometheusHttpServer.java

@@ -14,9 +14,11 @@
 import io.opentelemetry.sdk.common.CompletableResultCode;
 import io.opentelemetry.sdk.common.export.MemoryMode;
 import io.opentelemetry.sdk.internal.DaemonThreadFactory;
+import io.opentelemetry.sdk.metrics.Aggregation;
 import io.opentelemetry.sdk.metrics.InstrumentType;
 import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
 import io.opentelemetry.sdk.metrics.export.CollectionRegistration;
+import io.opentelemetry.sdk.metrics.export.DefaultAggregationSelector;
 import io.opentelemetry.sdk.metrics.export.MetricReader;
 import io.prometheus.metrics.exporter.httpserver.HTTPServer;
 import io.prometheus.metrics.model.registry.PrometheusRegistry;
@@ -41,6 +43,7 @@ public final class PrometheusHttpServer implements MetricReader {
   private final PrometheusRegistry prometheusRegistry;
   private final String host;
   private final MemoryMode memoryMode;
+  private final DefaultAggregationSelector defaultAggregationSelector;
 
   /**
    * Returns a new {@link PrometheusHttpServer} which can be registered to an {@link
@@ -65,7 +68,8 @@ public static PrometheusHttpServerBuilder builder() {
       boolean otelScopeEnabled,
       @Nullable Predicate<String> allowedResourceAttributesFilter,
       MemoryMode memoryMode,
-      @Nullable HttpHandler defaultHandler) {
+      @Nullable HttpHandler defaultHandler,
+      DefaultAggregationSelector defaultAggregationSelector) {
     this.builder = builder;
     this.prometheusMetricReader =
         new PrometheusMetricReader(otelScopeEnabled, allowedResourceAttributesFilter);
@@ -92,13 +96,19 @@ public static PrometheusHttpServerBuilder builder() {
     } catch (IOException e) {
       throw new UncheckedIOException("Could not create Prometheus HTTP server", e);
     }
+    this.defaultAggregationSelector = defaultAggregationSelector;
   }
 
   @Override
   public AggregationTemporality getAggregationTemporality(InstrumentType instrumentType) {
     return prometheusMetricReader.getAggregationTemporality(instrumentType);
   }
 
+  @Override
+  public Aggregation getDefaultAggregation(InstrumentType instrumentType) {
+    return defaultAggregationSelector.getDefaultAggregation(instrumentType);
+  }
+
   @Override
   public MemoryMode getMemoryMode() {
     return memoryMode;

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/PrometheusHttpServerBuilder.java

@@ -10,6 +10,9 @@
 
 import com.sun.net.httpserver.HttpHandler;
 import io.opentelemetry.sdk.common.export.MemoryMode;
+import io.opentelemetry.sdk.metrics.InstrumentType;
+import io.opentelemetry.sdk.metrics.export.DefaultAggregationSelector;
+import io.opentelemetry.sdk.metrics.export.MetricExporter;
 import io.prometheus.metrics.model.registry.PrometheusRegistry;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -31,6 +34,8 @@ public final class PrometheusHttpServerBuilder {
   @Nullable private ExecutorService executor;
   private MemoryMode memoryMode = DEFAULT_MEMORY_MODE;
   @Nullable private HttpHandler defaultHandler;
+  private DefaultAggregationSelector defaultAggregationSelector =
+      DefaultAggregationSelector.getDefault();
 
   PrometheusHttpServerBuilder() {}
 
@@ -126,6 +131,19 @@ public PrometheusHttpServerBuilder setDefaultHandler(HttpHandler defaultHandler)
     return this;
   }
 
+  /**
+   * Set the {@link DefaultAggregationSelector} used for {@link
+   * MetricExporter#getDefaultAggregation(InstrumentType)}.
+   *
+   * <p>If unset, defaults to {@link DefaultAggregationSelector#getDefault()}.
+   */
+  public PrometheusHttpServerBuilder setDefaultAggregationSelector(
+      DefaultAggregationSelector defaultAggregationSelector) {
+    requireNonNull(defaultAggregationSelector, "defaultAggregationSelector");
+    this.defaultAggregationSelector = defaultAggregationSelector;
+    return this;
+  }
+
   /**
    * Returns a new {@link PrometheusHttpServer} with the configuration of this builder which can be
    * registered with a {@link io.opentelemetry.sdk.metrics.SdkMeterProvider}.
@@ -140,6 +158,7 @@ public PrometheusHttpServer build() {
         otelScopeEnabled,
         allowedResourceAttributesFilter,
         memoryMode,
-        defaultHandler);
+        defaultHandler,
+        defaultAggregationSelector);
   }
 }

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/internal/PrometheusMetricReaderProvider.java

@@ -5,12 +5,19 @@
 
 package io.opentelemetry.exporter.prometheus.internal;
 
+import static io.opentelemetry.sdk.metrics.Aggregation.explicitBucketHistogram;
+
 import io.opentelemetry.exporter.internal.ExporterBuilderUtil;
 import io.opentelemetry.exporter.prometheus.PrometheusHttpServer;
 import io.opentelemetry.exporter.prometheus.PrometheusHttpServerBuilder;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigurationException;
 import io.opentelemetry.sdk.autoconfigure.spi.internal.ConfigurableMetricReaderProvider;
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.InstrumentType;
+import io.opentelemetry.sdk.metrics.export.DefaultAggregationSelector;
 import io.opentelemetry.sdk.metrics.export.MetricReader;
+import io.opentelemetry.sdk.metrics.internal.aggregator.AggregationUtil;
 
 /**
  * SPI implementation for {@link PrometheusHttpServer}.
@@ -32,6 +39,20 @@ public MetricReader createMetricReader(ConfigProperties config) {
     if (host != null) {
       prometheusBuilder.setHost(host);
     }
+    String defaultHistogramAggregation =
+        config.getString("otel.exporter.prometheus.metrics.default.histogram.aggregation");
+    if (defaultHistogramAggregation != null) {
+      if (AggregationUtil.aggregationName(Aggregation.base2ExponentialBucketHistogram())
+          .equalsIgnoreCase(defaultHistogramAggregation)) {
+        prometheusBuilder.setDefaultAggregationSelector(
+            DefaultAggregationSelector.getDefault()
+                .with(InstrumentType.HISTOGRAM, Aggregation.base2ExponentialBucketHistogram()));
+      } else if (!AggregationUtil.aggregationName(explicitBucketHistogram())
+          .equalsIgnoreCase(defaultHistogramAggregation)) {
+        throw new ConfigurationException(
+            "Unrecognized default histogram aggregation: " + defaultHistogramAggregation);
+      }
+    }
 
     ExporterBuilderUtil.configureExporterMemoryMode(config, prometheusBuilder::setMemoryMode);
 

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/PrometheusHttpServerTest.java

@@ -113,6 +113,9 @@ void invalidConfig() {
     assertThatThrownBy(() -> PrometheusHttpServer.builder().setHost(""))
         .isInstanceOf(IllegalArgumentException.class)
         .hasMessage("host must not be empty");
+    assertThatThrownBy(() -> PrometheusHttpServer.builder().setDefaultAggregationSelector(null))
+        .isInstanceOf(NullPointerException.class)
+        .hasMessage("defaultAggregationSelector");
   }
 
   @Test

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/internal/PrometheusMetricReaderProviderTest.java

@@ -7,14 +7,18 @@
 
 import static org.assertj.core.api.Assertions.as;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.when;
 
 import com.sun.net.httpserver.HttpServer;
 import io.opentelemetry.exporter.prometheus.PrometheusHttpServer;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigurationException;
 import io.opentelemetry.sdk.autoconfigure.spi.internal.DefaultConfigProperties;
 import io.opentelemetry.sdk.common.export.MemoryMode;
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.InstrumentType;
 import io.opentelemetry.sdk.metrics.export.MetricReader;
 import io.prometheus.metrics.exporter.httpserver.HTTPServer;
 import java.io.IOException;
@@ -59,6 +63,8 @@ void createMetricReader_Default() throws IOException {
                 assertThat(server.getAddress().getPort()).isEqualTo(9464);
               });
       assertThat(metricReader.getMemoryMode()).isEqualTo(MemoryMode.IMMUTABLE_DATA);
+      assertThat(metricReader.getDefaultAggregation(InstrumentType.HISTOGRAM))
+          .isEqualTo(Aggregation.defaultAggregation());
     }
   }
 
@@ -76,6 +82,9 @@ void createMetricReader_WithConfiguration() throws IOException {
     config.put("otel.exporter.prometheus.host", "localhost");
     config.put("otel.exporter.prometheus.port", String.valueOf(port));
     config.put("otel.java.experimental.exporter.memory_mode", "reusable_data");
+    config.put(
+        "otel.exporter.prometheus.metrics.default.histogram.aggregation",
+        "BASE2_EXPONENTIAL_BUCKET_HISTOGRAM");
 
     when(configProperties.getInt(any())).thenReturn(null);
     when(configProperties.getString(any())).thenReturn(null);
@@ -91,6 +100,22 @@ void createMetricReader_WithConfiguration() throws IOException {
                 assertThat(server.getAddress().getPort()).isEqualTo(port);
               });
       assertThat(metricReader.getMemoryMode()).isEqualTo(MemoryMode.REUSABLE_DATA);
+      assertThat(metricReader.getDefaultAggregation(InstrumentType.HISTOGRAM))
+          .isEqualTo(Aggregation.base2ExponentialBucketHistogram());
     }
   }
+
+  @Test
+  void createMetricReader_WithWrongConfiguration() throws IOException {
+    Map<String, String> config = new HashMap<>();
+    config.put("otel.exporter.prometheus.metrics.default.histogram.aggregation", "foo");
+
+    when(configProperties.getInt(any())).thenReturn(null);
+    when(configProperties.getString(any())).thenReturn(null);
+
+    assertThatThrownBy(
+            () -> provider.createMetricReader(DefaultConfigProperties.createFromMap(config)))
+        .isInstanceOf(ConfigurationException.class)
+        .hasMessageContaining("Unrecognized default histogram aggregation:");
+  }
 }