Add auto-configuration for Exemplars

See gh-32415

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/exemplars/ExemplarsAutoConfiguration.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.tracing.exemplars;
+
+import io.micrometer.tracing.Span;
+import io.micrometer.tracing.Tracer;
+import io.prometheus.client.exemplars.tracer.common.SpanContextSupplier;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.SmartInitializingSingleton;
+import org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus.PrometheusMetricsExportAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.tracing.ConditionalOnEnabledTracing;
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.context.annotation.Bean;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} for Prometheus Exemplars with
+ * Micrometer Tracing.
+ *
+ * @author Jonatan Ivanov
+ * @since 3.0.0
+ */
+@AutoConfiguration(before = PrometheusMetricsExportAutoConfiguration.class)
+@ConditionalOnClass({ Tracer.class, SpanContextSupplier.class })
+@ConditionalOnEnabledTracing
+public class ExemplarsAutoConfiguration {
+
+	@Bean
+	@ConditionalOnMissingBean
+	SpanContextSupplier spanContextSupplier(ObjectProvider<Tracer> tracerProvider) {
+		return new LazyTracingSpanContextSupplier(tracerProvider);
+	}
+
+	/**
+	 * Since the MeterRegistry can depend on the {@link Tracer} (Exemplars) and the
+	 * {@link Tracer} can depend on the MeterRegistry (recording metrics), this
+	 * {@link SpanContextSupplier} breaks the circle by lazily loading the {@link Tracer}.
+	 */
+	static class LazyTracingSpanContextSupplier implements SpanContextSupplier, SmartInitializingSingleton {
+
+		private final ObjectProvider<Tracer> tracerProvider;
+
+		private Tracer tracer;
+
+		LazyTracingSpanContextSupplier(ObjectProvider<Tracer> tracerProvider) {
+			this.tracerProvider = tracerProvider;
+		}
+
+		@Override
+		public String getTraceId() {
+			return this.tracer.currentSpan().context().traceId();
+		}
+
+		@Override
+		public String getSpanId() {
+			return this.tracer.currentSpan().context().spanId();
+		}
+
+		@Override
+		public boolean isSampled() {
+			return this.tracer != null && isSampled(this.tracer);
+		}
+
+		private boolean isSampled(Tracer tracer) {
+			Span currentSpan = tracer.currentSpan();
+			return currentSpan != null && currentSpan.context().sampled();
+		}
+
+		@Override
+		public void afterSingletonsInstantiated() {
+			this.tracer = this.tracerProvider.getIfAvailable();
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/exemplars/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Auto-configuration for Prometheus Exemplars with Micrometer Tracing.
+ */
+package org.springframework.boot.actuate.autoconfigure.tracing.exemplars;

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -101,6 +101,7 @@ org.springframework.boot.actuate.autoconfigure.trace.http.HttpTraceEndpointAutoC
 org.springframework.boot.actuate.autoconfigure.tracing.BraveAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.tracing.MicrometerTracingAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.tracing.OpenTelemetryAutoConfiguration
+org.springframework.boot.actuate.autoconfigure.tracing.exemplars.ExemplarsAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.tracing.wavefront.WavefrontTracingAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.tracing.zipkin.ZipkinAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.web.mappings.MappingsEndpointAutoConfiguration

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/exemplars/ExemplarsAutoConfigurationTests.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.tracing.exemplars;
+
+import io.micrometer.observation.Observation;
+import io.micrometer.observation.ObservationRegistry;
+import io.micrometer.prometheus.PrometheusMeterRegistry;
+import io.prometheus.client.exemplars.tracer.common.SpanContextSupplier;
+import io.prometheus.client.exporter.common.TextFormat;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus.PrometheusMetricsExportAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsRun;
+import org.springframework.boot.actuate.autoconfigure.observation.ObservationAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.tracing.BraveAutoConfiguration;
+import org.springframework.boot.actuate.autoconfigure.tracing.MicrometerTracingAutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.FilteredClassLoader;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link ExemplarsAutoConfiguration}.
+ *
+ * * @author Jonatan Ivanov
+ */
+class ExemplarsAutoConfigurationTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+			.withPropertyValues("management.tracing.sampling.probability=1.0",
+					"management.metrics.distribution.percentiles-histogram.all=true")
+			.with(MetricsRun.limitedTo(PrometheusMetricsExportAutoConfiguration.class)).withConfiguration(
+					AutoConfigurations.of(ExemplarsAutoConfiguration.class, ObservationAutoConfiguration.class,
+							BraveAutoConfiguration.class, MicrometerTracingAutoConfiguration.class));
+
+	@Test
+	void shouldNotSupplyBeansIfTracingIsDisabled() {
+		this.contextRunner.withPropertyValues("management.tracing.enabled=false")
+				.run((context) -> assertThat(context).doesNotHaveBean(SpanContextSupplier.class));
+	}
+
+	@Test
+	void shouldNotSupplyBeansIfPrometheusSupportIsMissing() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader("io.prometheus.client.exemplars"))
+				.run((context) -> assertThat(context).doesNotHaveBean(SpanContextSupplier.class));
+	}
+
+	@Test
+	void shouldNotSupplyBeansIfMicrometerTracingIsMissing() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader("io.micrometer.tracing"))
+				.run((context) -> assertThat(context).doesNotHaveBean(SpanContextSupplier.class));
+	}
+
+	@Test
+	void shouldSupplyCustomBeans() {
+		this.contextRunner.withUserConfiguration(CustomConfiguration.class)
+				.run((context) -> assertThat(context).hasSingleBean(SpanContextSupplier.class)
+						.getBean(SpanContextSupplier.class).isSameAs(CustomConfiguration.SUPPLIER));
+	}
+
+	@Test
+	void prometheusOpenMetricsOutputShouldContainExemplars() {
+		this.contextRunner.run((context) -> {
+			assertThat(context).hasSingleBean(SpanContextSupplier.class);
+			ObservationRegistry observationRegistry = context.getBean(ObservationRegistry.class);
+			Observation.start("test.observation", observationRegistry).stop();
+
+			PrometheusMeterRegistry prometheusMeterRegistry = context.getBean(PrometheusMeterRegistry.class);
+			String openMetricsOutput = prometheusMeterRegistry.scrape(TextFormat.CONTENT_TYPE_OPENMETRICS_100);
+			assertThat(openMetricsOutput).contains("test_observation_seconds_bucket").containsOnlyOnce("trace_id=")
+					.containsOnlyOnce("span_id=");
+		});
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	private static class CustomConfiguration {
+
+		static final SpanContextSupplier SUPPLIER = mock(SpanContextSupplier.class);
+
+		@Bean
+		SpanContextSupplier customSpanContextSupplier() {
+			return SUPPLIER;
+		}
+
+	}
+
+}