Add marker information to ECS structured logging

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/ElasticCommonSchemaStructuredLogFormatter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -17,8 +17,11 @@
 package org.springframework.boot.logging.log4j2;
 
 import java.util.Objects;
+import java.util.Set;
+import java.util.TreeSet;
 
 import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Marker;
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.core.impl.ThrowableProxy;
 import org.apache.logging.log4j.core.time.Instant;
@@ -66,11 +69,30 @@ private static void jsonMembers(Environment environment, JsonWriter.Members<LogE
 			thrownProxyMembers.add("error.message", ThrowableProxy::getMessage);
 			thrownProxyMembers.add("error.stack_trace", ThrowableProxy::getExtendedStackTraceAsString);
 		});
+		members.add("tags", LogEvent::getMarker)
+			.whenNotNull()
+			.as(ElasticCommonSchemaStructuredLogFormatter::getMarkers)
+			.whenNotEmpty();
 		members.add("ecs.version", "8.11");
 	}
 
 	private static java.time.Instant asTimestamp(Instant instant) {
 		return java.time.Instant.ofEpochMilli(instant.getEpochMillisecond()).plusNanos(instant.getNanoOfMillisecond());
 	}
 
+	private static Set<String> getMarkers(Marker marker) {
+		Set<String> result = new TreeSet<>();
+		addMarkers(result, marker);
+		return result;
+	}
+
+	private static void addMarkers(Set<String> result, Marker marker) {
+		result.add(marker.getName());
+		if (marker.hasParents()) {
+			for (Marker parent : marker.getParents()) {
+				addMarkers(result, parent);
+			}
+		}
+	}
+
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/ElasticCommonSchemaStructuredLogFormatter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,11 +16,16 @@
 
 package org.springframework.boot.logging.logback;
 
+import java.util.Iterator;
+import java.util.List;
 import java.util.Objects;
+import java.util.Set;
+import java.util.TreeSet;
 
 import ch.qos.logback.classic.pattern.ThrowableProxyConverter;
 import ch.qos.logback.classic.spi.ILoggingEvent;
 import ch.qos.logback.classic.spi.IThrowableProxy;
+import org.slf4j.Marker;
 import org.slf4j.event.KeyValuePair;
 
 import org.springframework.boot.json.JsonWriter;
@@ -69,6 +74,26 @@ private static void jsonMembers(Environment environment, ThrowableProxyConverter
 			throwableMembers.add("error.stack_trace", throwableProxyConverter::convert);
 		});
 		members.add("ecs.version", "8.11");
+		members.add("tags", ILoggingEvent::getMarkerList)
+			.whenNotNull()
+			.as(ElasticCommonSchemaStructuredLogFormatter::getMarkers)
+			.whenNotEmpty();
+	}
+
+	private static Set<String> getMarkers(List<Marker> markers) {
+		Set<String> result = new TreeSet<>();
+		addMarkers(result, markers.iterator());
+		return result;
+	}
+
+	private static void addMarkers(Set<String> result, Iterator<Marker> iterator) {
+		while (iterator.hasNext()) {
+			Marker marker = iterator.next();
+			result.add(marker.getName());
+			if (marker.hasReferences()) {
+				addMarkers(result, marker.iterator());
+			}
+		}
 	}
 
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/ElasticCommonSchemaStructuredLogFormatterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,8 +16,11 @@
 
 package org.springframework.boot.logging.log4j2;
 
+import java.util.List;
 import java.util.Map;
 
+import org.apache.logging.log4j.Marker;
+import org.apache.logging.log4j.MarkerManager;
 import org.apache.logging.log4j.core.impl.JdkMapAdapterStringMap;
 import org.apache.logging.log4j.core.impl.MutableLogEvent;
 import org.apache.logging.log4j.message.MapMessage;
@@ -100,4 +103,29 @@ void shouldFormatStructuredMessage() {
 				"org.example.Test", "message", expectedMessage, "ecs.version", "8.11"));
 	}
 
+	@Test
+	void shouldFormatMarkersAsTags() {
+		MutableLogEvent event = createEvent();
+
+		Marker parent = MarkerManager.getMarker("parent");
+		parent.addParents(MarkerManager.getMarker("grandparent"));
+
+		Marker parent1 = MarkerManager.getMarker("parent1");
+		parent1.addParents(MarkerManager.getMarker("grandparent1"));
+
+		Marker grandchild = MarkerManager.getMarker("grandchild");
+		grandchild.addParents(parent);
+		grandchild.addParents(parent1);
+		event.setMarker(grandchild);
+
+		String json = this.formatter.format(event);
+		assertThat(json).endsWith("\n");
+		Map<String, Object> deserialized = deserialize(json);
+		assertThat(deserialized).containsExactlyInAnyOrderEntriesOf(map("@timestamp", "2024-07-02T08:49:53Z",
+				"log.level", "INFO", "process.pid", 1, "process.thread.name", "main", "service.name", "name",
+				"service.version", "1.0.0", "service.environment", "test", "service.node.name", "node-1", "log.logger",
+				"org.example.Test", "message", "message", "ecs.version", "8.11", "tags",
+				List.of("grandchild", "grandparent", "grandparent1", "parent", "parent1")));
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/logback/ElasticCommonSchemaStructuredLogFormatterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -17,12 +17,15 @@
 package org.springframework.boot.logging.logback;
 
 import java.util.Collections;
+import java.util.List;
 import java.util.Map;
 
 import ch.qos.logback.classic.spi.LoggingEvent;
 import ch.qos.logback.classic.spi.ThrowableProxy;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Marker;
+import org.slf4j.MarkerFactory;
 
 import org.springframework.mock.env.MockEnvironment;
 
@@ -92,4 +95,30 @@ void shouldFormatException() {
 					.replace("\r", "\\r"));
 	}
 
+	@Test
+	void shouldFormatMarkersAsTags() {
+		LoggingEvent event = createEvent();
+		event.setMDCPropertyMap(Collections.emptyMap());
+
+		Marker parent = MarkerFactory.getDetachedMarker("parent");
+		parent.add(MarkerFactory.getDetachedMarker("child"));
+
+		Marker parent1 = MarkerFactory.getDetachedMarker("parent1");
+		parent1.add(MarkerFactory.getDetachedMarker("child1"));
+
+		Marker grandparent = MarkerFactory.getMarker("grandparent");
+		grandparent.add(parent);
+		grandparent.add(parent1);
+		event.addMarker(grandparent);
+
+		String json = this.formatter.format(event);
+		assertThat(json).endsWith("\n");
+		Map<String, Object> deserialized = deserialize(json);
+		assertThat(deserialized).containsExactlyInAnyOrderEntriesOf(
+				map("@timestamp", "2024-07-02T08:49:53Z", "log.level", "INFO", "process.pid", 1, "process.thread.name",
+						"main", "service.name", "name", "service.version", "1.0.0", "service.environment", "test",
+						"service.node.name", "node-1", "log.logger", "org.example.Test", "message", "message",
+						"ecs.version", "8.11", "tags", List.of("child", "child1", "grandparent", "parent", "parent1")));
+	}
+
 }