Add OTEL Semantic Conventions support

src/Elastic.CommonSchema.NLog/EcsLayout.cs

@@ -304,7 +304,9 @@ public NLogEcsDocument RenderEcsDocument(LogEventInfo logEvent)
 			ecsEvent.Event = GetEvent(logEvent);
 			ecsEvent.Process = GetProcess(logEvent);
 			ecsEvent.Tags = GetTags(logEvent);
+#pragma warning disable CS0618 // Obsolete Labels
 			ecsEvent.Labels = GetLabels(logEvent);
+#pragma warning restore CS0618
 			ecsEvent.Http = GetHttp(logEvent);
 			ecsEvent.Url = GetUrl(logEvent);
 

src/Elastic.CommonSchema/EcsDocument.Generated.cs

@@ -36,9 +36,10 @@ public partial class EcsDocument : BaseFieldSet , IAs, ICodeSignature, IElf, IEn
 		/// Container for additional metadata against this event.
 		/// <para/>
 		/// When working with unknown fields use <see cref="AssignField"/>. <br/>
-		/// <para> This will try to assign valid ECS fields to their respective property 
+		/// <para> This will try to assign valid ECS fields to their respective property
 		/// Failing that it will assign strings to <see cref="Labels"/> and everything else to <see cref="Metadata"/> </para>
 		/// </summary>
+		[Obsolete("Use Attributes instead. Metadata values will be merged into Attributes during serialization.")]
 		[JsonPropertyName("metadata"), DataMember(Name = "metadata")]
 		[JsonConverter(typeof(MetadataDictionaryConverter))]
 		public MetadataDictionary? Metadata { get; set; }

src/Elastic.CommonSchema/EcsDocument.OTel.cs

@@ -0,0 +1,41 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System.Collections.Generic;
+using System.Runtime.Serialization;
+using System.Text.Json.Serialization;
+
+namespace Elastic.CommonSchema;
+
+public partial class EcsDocument
+{
+	/// <summary>
+	/// Passthrough key-value store for OTel semantic convention attributes.
+	/// In Elasticsearch, <c>attributes</c> is a passthrough field type where the prefix can be omitted during queries.
+	/// In JSON source, data is nested under an <c>attributes</c> object.
+	/// </summary>
+	[JsonPropertyName("attributes"), DataMember(Name = "attributes")]
+	public MetadataDictionary? Attributes { get; set; }
+
+	/// <summary>
+	/// Assigns an OTel attribute value. Always stores in <see cref="Attributes"/>.
+	/// If the OTel name maps to an ECS field (via <see cref="OTelMappings.OTelToEcs"/>),
+	/// also sets the corresponding ECS property via <see cref="AssignField"/>.
+	/// </summary>
+	/// <param name="otelName">The OTel semantic convention attribute name</param>
+	/// <param name="value">The value to assign</param>
+	public void AssignOTelField(string otelName, object value)
+	{
+		// Always store in Attributes
+		Attributes ??= new MetadataDictionary();
+		Attributes[otelName] = value;
+
+		// If there's a mapping to an ECS field, also set it
+		if (OTelMappings.OTelToEcs.TryGetValue(otelName, out var ecsPath))
+			AssignField(ecsPath, value);
+		else
+			// For match relations, the OTel name IS the ECS name — try direct assignment
+			AssignField(otelName, value);
+	}
+}

src/Elastic.CommonSchema/EcsDocument.cs

@@ -97,6 +97,9 @@ public static TEcsDocument CreateNewWithDefaults<TEcsDocument>(
 		if (options?.IncludeActivityData is null or true)
 			SetActivityData(doc);
 
+		// Process remaining OTel resource attributes through the mapping table
+		ApplyOTelResourceAttributes(doc, initialCache.OTelResourceAttributes);
+
 		return doc;
 	}
 
@@ -121,6 +124,48 @@ private static IDictionary<string, string> ParseOTelResourceAttributes(string? r
 		return keyValues;
 	}
 
+	// Attributes already handled by specific code in GetService/GetHost
+	private static readonly HashSet<string> HandledResourceAttributes = new()
+	{
+		"service.name", "service.version", "service.instance.id",
+		"deployment.environment",
+		"host.name", "host.type", "host.arch"
+	};
+
+	private static void ApplyOTelResourceAttributes(EcsDocument doc, IDictionary<string, string>? resourceAttributes)
+	{
+		if (resourceAttributes == null || resourceAttributes.Count == 0) return;
+
+		foreach (var kvp in resourceAttributes)
+		{
+			var attrName = kvp.Key;
+			var attrValue = kvp.Value;
+
+			// Skip attributes already handled by specific code
+			if (HandledResourceAttributes.Contains(attrName)) continue;
+
+			// Check if this OTel attribute name maps to an ECS field
+			if (OTelMappings.OTelToEcs.TryGetValue(attrName, out var ecsPath))
+			{
+				// Equivalent mapping: set ECS property and store in Attributes
+				doc.AssignField(ecsPath, attrValue);
+				doc.Attributes ??= new MetadataDictionary();
+				doc.Attributes[attrName] = attrValue;
+			}
+			else if (OTelMappings.AllBidirectionalEcsFields.Contains(attrName))
+			{
+				// Match relation: OTel name IS the ECS name
+				doc.AssignField(attrName, attrValue);
+			}
+			else
+			{
+				// Unknown attribute: store in Attributes only
+				doc.Attributes ??= new MetadataDictionary();
+				doc.Attributes[attrName] = attrValue;
+			}
+		}
+	}
+
 
 	/// <summary>
 	/// Create an instance of <see cref="Agent"/> that defaults to the assembly from

src/Elastic.CommonSchema/FieldSets.Generated.cs

@@ -173,6 +173,7 @@ public abstract class BaseFieldSet {
 		/// Example: `docker` and `k8s` labels.</para>
 		/// <example>{"application": "foo-bar", "env": "production"}</example>
 		///</summary>
+		[Obsolete("Use EcsDocument.Attributes instead. Labels values will be merged into Attributes during serialization.")]
 		[JsonPropertyName("labels"), DataMember(Name = "labels")]
 		public Labels? Labels { get; set; }
 	}
@@ -605,6 +606,7 @@ public abstract class ContainerFieldSet {
 		/// <para>Image labels.</para>
 		/// <example></example>
 		///</summary>
+		[Obsolete("Use EcsDocument.Attributes instead. Labels values will be merged into Attributes during serialization.")]
 		[JsonPropertyName("labels"), DataMember(Name = "labels")]
 		public ContainerLabels? Labels { get; set; }
 	}

src/Elastic.CommonSchema/IndexComponents.Generated.cs

@@ -345,6 +345,10 @@ public static class IndexComponents
         ""@timestamp"": {
           ""type"": ""date""
         },
+        ""attributes"": {
+          ""type"": ""passthrough"",
+          ""priority"": 10
+        },
         ""labels"": {
           ""type"": ""object""
         },
@@ -359,8 +363,7 @@ public static class IndexComponents
       }
     }
   }
-}
-"
+}"
 			},
 		{	
 				"ecs_9.3.0_client", 

src/Elastic.CommonSchema/IndexTemplates.Generated.cs

@@ -110,7 +110,7 @@ public static string GetIndexTemplateForElasticsearchComposable(string indexPatt
         ""codec"": ""best_compression"",
         ""mapping"": {
           ""total_fields"": {
-            ""limit"": 3000
+            ""limit"": 3212
           }
         }
       }
@@ -9562,7 +9562,7 @@ public static string GetIndexTemplateForElasticsearchLegacy(string indexPattern
     ""index"": {
       ""mapping"": {
         ""total_fields"": {
-          ""limit"": 10000
+          ""limit"": 3212
         }
       },
       ""refresh_interval"": ""5s""