Add experimental autoconfigure support for customizing cardinality limit

sdk-extensions/autoconfigure/README.md

@@ -292,6 +292,12 @@ These properties can be used to control the maximum size of spans by placing lim
 |------------------------------|------------------------------|-----------------------------------------------------------------------------------------------------------------|
 | otel.metrics.exemplar.filter | OTEL_METRICS_EXEMPLAR_FILTER | The filter for exemplar sampling.  Can be `ALWAYS_OFF`, `ALWAYS_ON` or `TRACE_BASED`. Default is `TRACE_BASED`. |
 
+## Cardinality Limits
+
+| System property                             | Environment variable                        | Description                                                                                                                               |
+|---------------------------------------------|---------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
+| otel.experimental.metrics.cardinality.limit | OTEL_EXPERIMENTAL_METRICS_CARDINALITY_LIMIT | If set, configure experimental cardinality limit. The value dictates the maximum number of distinct points per metric. Default is `2000`. |
+
 ## Periodic Metric Reader
 
 | System property             | Environment variable        | Description                                                                                  |

sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/MeterProviderConfiguration.java

@@ -13,6 +13,7 @@
 import io.opentelemetry.sdk.metrics.export.MetricReader;
 import io.opentelemetry.sdk.metrics.internal.SdkMeterProviderUtil;
 import io.opentelemetry.sdk.metrics.internal.exemplar.ExemplarFilter;
+import io.opentelemetry.sdk.metrics.internal.state.MetricStorage;
 import java.io.Closeable;
 import java.util.Collections;
 import java.util.List;
@@ -48,8 +49,18 @@ static void configureMeterProvider(
         break;
     }
 
+    int cardinalityLimit =
+        config.getInt(
+            "otel.experimental.metrics.cardinality.limit", MetricStorage.DEFAULT_MAX_CARDINALITY);
+    if (cardinalityLimit < 1) {
+      throw new ConfigurationException("otel.experimental.metrics.cardinality.limit must be >= 1");
+    }
+
     configureMetricReaders(config, serviceClassLoader, metricExporterCustomizer, closeables)
-        .forEach(meterProviderBuilder::registerMetricReader);
+        .forEach(
+            reader ->
+                SdkMeterProviderUtil.registerMetricReaderWithCardinalitySelector(
+                    meterProviderBuilder, reader, instrumentType -> cardinalityLimit));
   }
 
   static List<MetricReader> configureMetricReaders(

sdk-extensions/autoconfigure/src/testFullConfig/java/io/opentelemetry/sdk/autoconfigure/MeterProviderConfigurationTest.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.autoconfigure;
+
+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 com.google.common.collect.ImmutableMap;
+import io.opentelemetry.internal.testing.CleanupExtension;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigurationException;
+import io.opentelemetry.sdk.autoconfigure.spi.internal.DefaultConfigProperties;
+import io.opentelemetry.sdk.metrics.InstrumentType;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.SdkMeterProviderBuilder;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
+import io.opentelemetry.sdk.metrics.internal.export.CardinalityLimitSelector;
+import java.io.Closeable;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+class MeterProviderConfigurationTest {
+
+  @RegisterExtension CleanupExtension cleanup = new CleanupExtension();
+
+  @Test
+  void configureMeterProvider_InvalidCardinalityLimit() {
+    List<Closeable> closeables = new ArrayList<>();
+
+    assertThatThrownBy(
+            () -> {
+              MeterProviderConfiguration.configureMeterProvider(
+                  SdkMeterProvider.builder(),
+                  DefaultConfigProperties.createForTest(
+                      ImmutableMap.of(
+                          "otel.metrics.exporter",
+                          "logging",
+                          "otel.experimental.metrics.cardinality.limit",
+                          "0")),
+                  MeterProviderConfigurationTest.class.getClassLoader(),
+                  (a, b) -> a,
+                  closeables);
+            })
+        .isInstanceOf(ConfigurationException.class)
+        .hasMessage("otel.experimental.metrics.cardinality.limit must be >= 1");
+    cleanup.addCloseables(closeables);
+  }
+
+  @Test
+  void configureMeterProvider_ConfiguresCardinalityLimit() {
+    List<Closeable> closeables = new ArrayList<>();
+
+    // Verify default cardinality
+    SdkMeterProviderBuilder builder = SdkMeterProvider.builder();
+    MeterProviderConfiguration.configureMeterProvider(
+        builder,
+        DefaultConfigProperties.createForTest(
+            Collections.singletonMap("otel.metrics.exporter", "logging")),
+        MeterProviderConfigurationTest.class.getClassLoader(),
+        (a, b) -> a,
+        closeables);
+    cleanup.addCloseables(closeables);
+    assertCardinalityLimit(builder, 2000);
+
+    // Customized limit cardinality limit to 100
+    builder = SdkMeterProvider.builder();
+    MeterProviderConfiguration.configureMeterProvider(
+        builder,
+        DefaultConfigProperties.createForTest(
+            ImmutableMap.of(
+                "otel.metrics.exporter",
+                "logging",
+                "otel.experimental.metrics.cardinality.limit",
+                "100")),
+        MeterProviderConfigurationTest.class.getClassLoader(),
+        (a, b) -> a,
+        closeables);
+    cleanup.addCloseables(closeables);
+    assertCardinalityLimit(builder, 100);
+  }
+
+  private static void assertCardinalityLimit(
+      SdkMeterProviderBuilder builder, int expectedCardinalityLimit) {
+    assertThat(builder)
+        .extracting(
+            "metricReaders",
+            as(InstanceOfAssertFactories.map(MetricReader.class, CardinalityLimitSelector.class)))
+        .hasSizeGreaterThan(0)
+        .allSatisfy(
+            (metricReader, cardinalityLimitSelector) -> {
+              for (InstrumentType instrumentType : InstrumentType.values()) {
+                assertThat(cardinalityLimitSelector.getCardinalityLimit(instrumentType))
+                    .isEqualTo(expectedCardinalityLimit);
+              }
+            });
+  }
+}