Add baggage tag fields to spans with OpenTelemetry

With OpenTelemetry, fields listed in management.tracing.baggage.tag-fields
only became span tags when the application itself touched the baggage
through the Tracer API. Baggage that arrived with a request was
propagated correctly, but spans were not tagged with it (see
micrometer-metrics/tracing#933).

This commit registers Micrometer Tracing's BaggageTaggingSpanProcessor
whenever baggage is enabled and at least one tag field is configured, so
that spans are tagged with the baggage that is present in their parent
context. A custom BaggageTaggingSpanProcessor bean backs off the
auto-configured one. The tag-fields property is now also mentioned in
the baggage section of the tracing documentation.

See gh-51656

Signed-off-by: Oleksandr Shevchenko <oleksandr.shevchenko@datarobot.com>

module/spring-boot-micrometer-tracing-opentelemetry/src/main/java/org/springframework/boot/micrometer/tracing/opentelemetry/autoconfigure/OpenTelemetryPropagationConfigurations.java

@@ -18,18 +18,22 @@ package org.springframework.boot.micrometer.tracing.opentelemetry.autoconfigure;
 
 import java.util.List;
 
+import io.micrometer.tracing.otel.bridge.BaggageTaggingSpanProcessor;
 import io.micrometer.tracing.otel.bridge.OtelBaggageManager;
 import io.micrometer.tracing.otel.bridge.OtelCurrentTraceContext;
 import io.micrometer.tracing.otel.bridge.Slf4JBaggageEventListener;
 import io.micrometer.tracing.otel.propagation.BaggageTextMapPropagator;
 import io.opentelemetry.context.propagation.TextMapPropagator;
 
+import org.springframework.boot.autoconfigure.condition.ConditionMessage;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBooleanProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.OnPropertyListCondition;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.micrometer.tracing.autoconfigure.ConditionalOnEnabledTracingExport;
 import org.springframework.boot.micrometer.tracing.autoconfigure.TracingProperties;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 
 /**
@@ -37,6 +41,7 @@ import org.springframework.context.annotation.Configuration;
  * {@link OpenTelemetryTracingAutoConfiguration}.
  *
  * @author Moritz Halbritter
+ * @author Oleksandr Shevchenko
  */
 class OpenTelemetryPropagationConfigurations {
 
@@ -87,6 +92,26 @@ class OpenTelemetryPropagationConfigurations {
 			return new Slf4JBaggageEventListener(this.tracingProperties.getBaggage().getCorrelation().getFields());
 		}
 
+		@Bean
+		@ConditionalOnMissingBean
+		@Conditional(OnBaggageTagFieldsCondition.class)
+		BaggageTaggingSpanProcessor otelBaggageTaggingSpanProcessor() {
+			return new BaggageTaggingSpanProcessor(this.tracingProperties.getBaggage().getTagFields());
+		}
+
+		/**
+		 * Condition that matches when {@code management.tracing.baggage.tag-fields} has
+		 * at least one entry.
+		 */
+		static class OnBaggageTagFieldsCondition extends OnPropertyListCondition {
+
+			OnBaggageTagFieldsCondition() {
+				super("management.tracing.baggage.tag-fields",
+						() -> ConditionMessage.forCondition("Baggage tag fields"));
+			}
+
+		}
+
 	}
 
 	/**

module/spring-boot-micrometer-tracing-opentelemetry/src/test/java/org/springframework/boot/micrometer/tracing/opentelemetry/autoconfigure/OpenTelemetryTracingAutoConfigurationTests.java

@@ -30,6 +30,7 @@ import io.micrometer.tracing.SpanCustomizer;
 import io.micrometer.tracing.Tracer.SpanInScope;
 import io.micrometer.tracing.handler.PropagatingReceiverTracingObservationHandler;
 import io.micrometer.tracing.handler.PropagatingSenderTracingObservationHandler;
+import io.micrometer.tracing.otel.bridge.BaggageTaggingSpanProcessor;
 import io.micrometer.tracing.otel.bridge.EventListener;
 import io.micrometer.tracing.otel.bridge.OtelCurrentTraceContext;
 import io.micrometer.tracing.otel.bridge.OtelPropagator;
@@ -40,18 +41,21 @@ import io.micrometer.tracing.otel.bridge.Slf4JBaggageEventListener;
 import io.micrometer.tracing.otel.bridge.Slf4JEventListener;
 import io.micrometer.tracing.otel.propagation.BaggageTextMapPropagator;
 import io.micrometer.tracing.propagation.Propagator;
+import io.opentelemetry.api.baggage.Baggage;
 import io.opentelemetry.api.common.AttributeKey;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.metrics.MeterProvider;
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.Tracer;
 import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
+import io.opentelemetry.context.Scope;
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.context.propagation.TextMapPropagator;
 import io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporter;
 import io.opentelemetry.extension.trace.propagation.B3Propagator;
 import io.opentelemetry.sdk.common.CompletableResultCode;
 import io.opentelemetry.sdk.resources.Resource;
+import io.opentelemetry.sdk.trace.ReadableSpan;
 import io.opentelemetry.sdk.trace.SdkTracerProvider;
 import io.opentelemetry.sdk.trace.SpanLimits;
 import io.opentelemetry.sdk.trace.SpanProcessor;
@@ -91,6 +95,7 @@ import static org.mockito.Mockito.mock;
  * @author Moritz Halbritter
  * @author Andy Wilkinson
  * @author Yanming Zhou
+ * @author Oleksandr Shevchenko
  */
 class OpenTelemetryTracingAutoConfigurationTests {
 
@@ -390,6 +395,54 @@ class OpenTelemetryTracingAutoConfigurationTests {
 			});
 	}
 
+	@Test
+	void shouldSupplyBaggageTaggingSpanProcessorWhenTagFieldsAreConfigured() {
+		this.contextRunner.withPropertyValues("management.tracing.baggage.tag-fields=t1,t2").run((context) -> {
+			assertThat(context).hasSingleBean(BaggageTaggingSpanProcessor.class);
+			SpanProcessors spanProcessors = context.getBean(SpanProcessors.class);
+			assertThat(spanProcessors).anyMatch(BaggageTaggingSpanProcessor.class::isInstance);
+		});
+	}
+
+	@Test
+	void shouldNotSupplyBaggageTaggingSpanProcessorWhenTagFieldsAreNotConfigured() {
+		this.contextRunner.run((context) -> assertThat(context).doesNotHaveBean(BaggageTaggingSpanProcessor.class));
+	}
+
+	@Test
+	void shouldNotSupplyBaggageTaggingSpanProcessorWhenBaggageDisabled() {
+		this.contextRunner
+			.withPropertyValues("management.tracing.baggage.enabled=false", "management.tracing.baggage.tag-fields=t1")
+			.run((context) -> assertThat(context).doesNotHaveBean(BaggageTaggingSpanProcessor.class));
+	}
+
+	@Test
+	void shouldBackOffOnCustomBaggageTaggingSpanProcessor() {
+		this.contextRunner.withPropertyValues("management.tracing.baggage.tag-fields=t1")
+			.withUserConfiguration(CustomBaggageTaggingSpanProcessorConfiguration.class)
+			.run((context) -> {
+				assertThat(context).hasBean("customBaggageTaggingSpanProcessor");
+				assertThat(context).hasSingleBean(BaggageTaggingSpanProcessor.class);
+			});
+	}
+
+	@Test
+	void baggageTaggingSpanProcessorShouldTagSpansWithBaggageFromParentContext() {
+		this.contextRunner
+			.withPropertyValues("management.tracing.baggage.tag-fields=t1",
+					"management.tracing.sampling.probability=1.0")
+			.run((context) -> {
+				Tracer tracer = context.getBean(Tracer.class);
+				try (Scope scope = Baggage.builder().put("t1", "v1").put("other", "v2").build().makeCurrent()) {
+					Span span = tracer.spanBuilder("test").startSpan();
+					span.end();
+					assertThat(span).isInstanceOf(ReadableSpan.class);
+					assertThat(((ReadableSpan) span).getAttribute(AttributeKey.stringKey("t1"))).isEqualTo("v1");
+					assertThat(((ReadableSpan) span).getAttribute(AttributeKey.stringKey("other"))).isNull();
+				}
+			});
+	}
+
 	@Test
 	void spanLimitsShouldBeConfiguredWithCustomProperties() {
 		this.contextRunner
@@ -608,6 +661,16 @@ class OpenTelemetryTracingAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	private static final class CustomBaggageTaggingSpanProcessorConfiguration {
+
+		@Bean
+		BaggageTaggingSpanProcessor customBaggageTaggingSpanProcessor() {
+			return new BaggageTaggingSpanProcessor(List.of("custom"));
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	private static final class AdditionalSpanProcessorConfiguration {