Switch reactor context propagation from auto to limited

- Polish
- Fix @since tags
- Add a test case
- Update context-propagation version

Closes gh-34201

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/ReactorAutoConfiguration.java

@@ -27,14 +27,14 @@ import org.springframework.context.annotation.Configuration;
  * {@link EnableAutoConfiguration Auto-configuration} for Reactor.
  *
  * @author Brian Clozel
- * @since 3.0.2
+ * @since 3.2.0
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnClass(Hooks.class)
 @EnableConfigurationProperties(ReactorProperties.class)
 public class ReactorAutoConfiguration {
 
-	public ReactorAutoConfiguration(ReactorProperties properties) {
+	ReactorAutoConfiguration(ReactorProperties properties) {
 		if (properties.getContextPropagation() == ReactorProperties.ContextPropagationMode.AUTO) {
 			Hooks.enableAutomaticContextPropagation();
 		}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/ReactorProperties.java

@@ -22,7 +22,7 @@ import org.springframework.boot.context.properties.ConfigurationProperties;
  * Configuration properties for Reactor.
  *
  * @author Brian Clozel
- * @since 3.0.3
+ * @since 3.2.0
  */
 @ConfigurationProperties(prefix = "spring.reactor")
 public class ReactorProperties {
@@ -30,7 +30,7 @@ public class ReactorProperties {
 	/**
 	 * Context Propagation support mode for Reactor operators.
 	 */
-	private ContextPropagationMode contextPropagation = ContextPropagationMode.AUTO;
+	private ContextPropagationMode contextPropagation = ContextPropagationMode.LIMITED;
 
 	public ContextPropagationMode getContextPropagation() {
 		return this.contextPropagation;

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -2092,7 +2092,7 @@
     },
     {
       "name": "spring.reactor.context-propagation",
-      "defaultValue": "auto"
+      "defaultValue": "limited"
     },
     {
       "name": "spring.reactor.stacktrace-mode.enabled",

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/reactor/ReactorAutoConfigurationTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.autoconfigure.reactor;
 import java.util.concurrent.atomic.AtomicReference;
 
 import io.micrometer.context.ContextRegistry;
+import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import reactor.core.publisher.Mono;
@@ -33,6 +34,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link ReactorAutoConfiguration}.
  *
  * @author Brian Clozel
+ * @author Moritz Halbritter
  */
 class ReactorAutoConfigurationTests {
 
@@ -41,7 +43,7 @@ class ReactorAutoConfigurationTests {
 
 	private static final String THREADLOCAL_KEY = "ReactorAutoConfigurationTests";
 
-	private static final ThreadLocal<String> THREADLOCAL_VALUE = ThreadLocal.withInitial(() -> "failure");
+	private static final ThreadLocal<String> THREADLOCAL_VALUE = ThreadLocal.withInitial(() -> "initial");
 
 	@BeforeAll
 	static void initializeThreadLocalAccessors() {
@@ -49,15 +51,33 @@ class ReactorAutoConfigurationTests {
 		globalRegistry.registerThreadLocalAccessor(THREADLOCAL_KEY, THREADLOCAL_VALUE);
 	}
 
+	@AfterAll
+	static void removeThreadLocalAccessors() {
+		ContextRegistry globalRegistry = ContextRegistry.getInstance();
+		globalRegistry.removeThreadLocalAccessor(THREADLOCAL_KEY);
+	}
+
 	@Test
-	void shouldConfigureAutomaticContextPropagation() {
+	void shouldNotConfigurePropagationByDefault() {
 		AtomicReference<String> threadLocalValue = new AtomicReference<>();
 		this.contextRunner.run((applicationContext) -> {
 			Mono.just("test")
 				.doOnNext((element) -> threadLocalValue.set(THREADLOCAL_VALUE.get()))
-				.contextWrite(Context.of(THREADLOCAL_KEY, "success"))
+				.contextWrite(Context.of(THREADLOCAL_KEY, "updated"))
+				.block();
+			assertThat(threadLocalValue.get()).isEqualTo("initial");
+		});
+	}
+
+	@Test
+	void shouldConfigurePropagationIfSetToAuto() {
+		AtomicReference<String> threadLocalValue = new AtomicReference<>();
+		this.contextRunner.withPropertyValues("spring.reactor.context-propagation=auto").run((applicationContext) -> {
+			Mono.just("test")
+				.doOnNext((element) -> threadLocalValue.set(THREADLOCAL_VALUE.get()))
+				.contextWrite(Context.of(THREADLOCAL_KEY, "updated"))
 				.block();
-			assertThat(threadLocalValue.get()).isEqualTo("success");
+			assertThat(threadLocalValue.get()).isEqualTo("updated");
 		});
 	}
 

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/observability.adoc

@@ -14,7 +14,11 @@ NOTE: Low cardinality key-values will be added to metrics and traces, while high
 Beans of type `ObservationPredicate`, `GlobalObservationConvention`, `ObservationFilter` and `ObservationHandler` will be automatically registered on the `ObservationRegistry`.
 You can additionally register any number of `ObservationRegistryCustomizer` beans to further configure the registry.
 
-For more details please see the https://micrometer.io/docs/observation[Micrometer Observation documentation].
+Observability support relies on the https://github.com/micrometer-metrics/context-propagation[Context Propagation library] for forwarding the current observation across threads and reactive pipelines.
+By default, `ThreadLocal` values are not automatically reinstated in reactive operators.
+This behavior is controlled with the configprop:spring.reactor.context-propagation[] property, which can be set to `auto` to enable automatic propagation.
+
+For more details about observations please see the https://micrometer.io/docs/observation[Micrometer Observation documentation].
 
 TIP: Observability for JDBC can be configured using a separate project.
 The https://github.com/jdbc-observations/datasource-micrometer[Datasource Micrometer project] provides a Spring Boot starter which automatically creates observations when JDBC operations are invoked.
@@ -80,7 +84,4 @@ The attributes of the `Resource` can be configured via the configprop:management
 NOTE: Spring Boot does not provide auto-configuration for OpenTelemetry metrics or logging.
 OpenTelemetry tracing is only auto-configured when used together with <<actuator#actuator.micrometer-tracing, Micrometer Tracing>>.
 
-Observability support relies on the https://github.com/micrometer-metrics/context-propagation[Context Propagation library] for forwarding the current observation across threads and reactive pipelines.
-`ThreadLocal` values are automatically reinstated in reactive operators, this behavior is controlled with the configprop:spring.reactor.context-propagation[] property.
-
 The next sections will provide more details about logging, metrics and traces.

spring-boot-project/spring-boot-parent/build.gradle

@@ -138,7 +138,7 @@ bom {
 			]
 		}
 	}
-	library("Micrometer Context Propagation", "1.0.2") {
+	library("Micrometer Context Propagation", "1.0.5") {
 		group("io.micrometer") {
 			modules = [
 					"context-propagation"