feat: add OpenTelemetry trace correlation for LoggerFactoryLogger

.github/workflows/pr_validation.yml

@@ -47,7 +47,7 @@ jobs:
 
       - name: "dotnet test"
         shell: bash
-        run: dotnet test -c Release 
+        run: dotnet test -c Release
 
       - name: "dotnet pack"
         run: dotnet pack -c Release -o ./bin/nuget

Akka.Hosting.sln

@@ -44,6 +44,10 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Akka.Remote.Hosting.Tests",
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Akka.Hosting.LoggingDemo", "src\Examples\Akka.Hosting.LoggingDemo\Akka.Hosting.LoggingDemo.csproj", "{298D7727-FDC6-49B2-9030-CC7F0E09B0B8}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Akka.Hosting.OpenTelemetry.Demo", "src\Examples\Akka.Hosting.OpenTelemetry.Demo\Akka.Hosting.OpenTelemetry.Demo.csproj", "{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Akka.Hosting.OpenTelemetry.AppHost", "src\Examples\Akka.Hosting.OpenTelemetry.AppHost\Akka.Hosting.OpenTelemetry.AppHost.csproj", "{CC22F505-B648-420E-BC8A-0FCE46082986}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -110,6 +114,14 @@ Global
 		{298D7727-FDC6-49B2-9030-CC7F0E09B0B8}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{298D7727-FDC6-49B2-9030-CC7F0E09B0B8}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{298D7727-FDC6-49B2-9030-CC7F0E09B0B8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2}.Release|Any CPU.Build.0 = Release|Any CPU
+		{CC22F505-B648-420E-BC8A-0FCE46082986}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CC22F505-B648-420E-BC8A-0FCE46082986}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CC22F505-B648-420E-BC8A-0FCE46082986}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CC22F505-B648-420E-BC8A-0FCE46082986}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -118,6 +130,8 @@ Global
 		{5F6A7BE8-6906-46CE-BA1C-72EA11EFA33B} = {EFA970FF-6BCC-4C38-84D8-324D40F2BF03}
 		{4F79325B-9EE7-4501-800F-7A1F8DFBCC80} = {EFA970FF-6BCC-4C38-84D8-324D40F2BF03}
 		{298D7727-FDC6-49B2-9030-CC7F0E09B0B8} = {EFA970FF-6BCC-4C38-84D8-324D40F2BF03}
+		{6BCB9636-DAD2-4364-8A83-3D2888FE5AB2} = {EFA970FF-6BCC-4C38-84D8-324D40F2BF03}
+		{CC22F505-B648-420E-BC8A-0FCE46082986} = {EFA970FF-6BCC-4C38-84D8-324D40F2BF03}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {B99E6BB8-642A-4A68-86DF-69567CBA700A}

Directory.Build.props

@@ -3,12 +3,16 @@
     <Copyright>Copyright © 2013-$([System.DateTime]::Now.Year) Akka.NET Team</Copyright>
     <Authors>Akka.NET Team</Authors>
     <VersionPrefix>1.5.59</VersionPrefix>
-    <PackageReleaseNotes>**Bug Fixes**
+    <PackageReleaseNotes>**New Features**
+* [Add OpenTelemetry trace correlation support for LoggerFactoryLogger](https://github.com/akkadotnet/Akka.Hosting/issues/700) - enables proper trace correlation for logs emitted from actor code. When using Akka.NET 1.5.59+, `LogEvent.ActivityContext` captures trace context at log creation time and flows it through to OpenTelemetry `LogRecord`s via the new `AkkaTraceContextProcessor`.
+
+**Bug Fixes**
 * [Fix semantic logging not capturing named placeholders as structured properties](https://github.com/akkadotnet/Akka.Hosting/pull/702) - resolved [issue #701](https://github.com/akkadotnet/Akka.Hosting/issues/701) where named placeholders like `{Event}` in log messages were not captured as searchable structured properties. Made all `LoggerConfigBuilder` properties optional and refactored message formatting code.
 * [Fix TestKit startup timeout race condition](https://github.com/akkadotnet/Akka.Hosting/pull/705) - resolved race condition in `TestKit.InitializeAsync()` where `CancellationTokenSource.Register()` threw exceptions on the timer thread, causing unhandled exceptions that crashed the test host process. Also increased default startup timeout from 10s to 30s for CI environments.
 
 **Updates**
-* [Bump Akka version from 1.5.58 to 1.5.59](https://github.com/akkadotnet/akka.net/releases/tag/1.5.59)</PackageReleaseNotes>
+* [Bump Akka version from 1.5.58 to 1.5.59](https://github.com/akkadotnet/akka.net/releases/tag/1.5.59)
+* Added OpenTelemetry dependency (1.9.0+) for trace correlation support</PackageReleaseNotes>
     <PackageIcon>akkalogo.png</PackageIcon>
     <PackageProjectUrl>
       https://github.com/akkadotnet/Akka.Hosting
@@ -31,8 +35,8 @@
     <CoverletVersion>6.0.3</CoverletVersion>
     <XunitRunneVisualstudio>3.1.5</XunitRunneVisualstudio>
     <AkkaVersion>1.5.59</AkkaVersion>
-    <MicrosoftExtensionsVersion>[6.0.0,)</MicrosoftExtensionsVersion>
-    <SystemTextJsonVersion>[6.0.10,)</SystemTextJsonVersion>
+    <MicrosoftExtensionsVersion>[8.0.0,)</MicrosoftExtensionsVersion>
+    <SystemTextJsonVersion>[8.0.5,)</SystemTextJsonVersion>
   </PropertyGroup>
   <!-- SourceLink support for all Akka.NET projects -->
   <ItemGroup>
@@ -50,4 +54,4 @@
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
   </PropertyGroup>
-</Project>
+</Project>

README.md

@@ -26,6 +26,7 @@ See the ["Introduction to Akka.Hosting - HOCON-less, "Pit of Success" Akka.NET R
     * [Microsoft.Extensions.Logging.ILoggerFactory Logging Support](#microsoftextensionsloggingiloggerfactory-logging-support)
     * [Serilog Support](#serilog-support)
     * [Microsoft.Extensions.Logging Log Event Filtering](#microsoftextensionslogging-log-event-filtering)
+- [OpenTelemetry Trace Correlation](#opentelemetry-trace-correlation)
 - [Microsoft.Extensions.Diagnostics.HealthChecks Integration](#healthchecks)
     * [Dependency Injected Health Checks](#healthcheck-di)
     * [Built-in HealthChecks](#healthcheck-builtin)
@@ -629,6 +630,46 @@ To set up the `Microsoft.Extensions.Logging` log filtering, you will need to edi
 
 [Back to top](#akkahosting)
 
+<a id="opentelemetry-trace-correlation"></a>
+# OpenTelemetry Trace Correlation
+
+Akka.NET processes log events asynchronously, which means `Activity.Current` does not flow across actor mailbox boundaries. To preserve trace correlation, Akka.Hosting captures the `ActivityContext` at log creation time and includes it in the log state. The `AkkaTraceContextProcessor` then applies that context to OpenTelemetry `LogRecord`s so exporters can correlate logs with traces.
+
+Minimal setup:
+
+```csharp
+using Akka.Hosting;
+using Akka.Hosting.Logging;
+using OpenTelemetry.Logs;
+using OpenTelemetry.Resources;
+
+builder.Logging.AddOpenTelemetry(options =>
+{
+    options.SetResourceBuilder(ResourceBuilder.CreateDefault()
+        .AddService("my-service"));
+
+    // Register before exporters
+    options.AddAkkaTraceCorrelation();
+
+    // Add OTLP exporter if you have not configured it elsewhere.
+    // Your mileage may vary; use the OpenTelemetry configuration that fits your app.
+    options.AddOtlpExporter();
+});
+
+builder.Services.AddAkka("MySystem", configBuilder =>
+{
+    configBuilder.ConfigureLoggers(setup =>
+    {
+        setup.ClearLoggers();
+        setup.AddLoggerFactory();
+    });
+});
+```
+
+See the demo in `src/Examples/Akka.Hosting.OpenTelemetry.AppHost` and `src/Examples/Akka.Hosting.OpenTelemetry.Demo` for a working Aspire setup.
+
+[Back to top](#akkahosting)
+
 <a id="filtering-logs"></a>
 ## Filtering Logs In Akka.NET
 

RELEASE_NOTES.md

@@ -1,11 +1,15 @@
-#### 1.5.59 January 26th 2026 ####
+#### 1.5.59 January 2026 ####
+
+**New Features**
+* [Add OpenTelemetry trace correlation support for LoggerFactoryLogger](https://github.com/akkadotnet/Akka.Hosting/issues/700) - enables proper trace correlation for logs emitted from actor code. Solves the problem that `Activity.Current` doesn't flow across actor mailbox boundaries because it uses `AsyncLocal<T>`. When using Akka.NET 1.5.59+, `LogEvent.ActivityContext` captures trace context at log creation time and flows it through to OpenTelemetry `LogRecord`s via the new `AkkaTraceContextProcessor`. Register with `options.AddAkkaTraceCorrelation()` in your OpenTelemetry logging configuration.
 
 **Bug Fixes**
 * [Fix semantic logging not capturing named placeholders as structured properties](https://github.com/akkadotnet/Akka.Hosting/pull/702) - resolved [issue #701](https://github.com/akkadotnet/Akka.Hosting/issues/701) where named placeholders like `{Event}` in log messages were not captured as searchable structured properties. Made all `LoggerConfigBuilder` properties optional and refactored message formatting code.
 * [Fix TestKit startup timeout race condition](https://github.com/akkadotnet/Akka.Hosting/pull/705) - resolved race condition in `TestKit.InitializeAsync()` where `CancellationTokenSource.Register()` threw exceptions on the timer thread, causing unhandled exceptions that crashed the test host process. Also increased default startup timeout from 10s to 30s for CI environments.
 
 **Updates**
 * [Bump Akka version from 1.5.58 to 1.5.59](https://github.com/akkadotnet/akka.net/releases/tag/1.5.59)
+* Added `OpenTelemetry` package dependency (1.9.0+) for trace correlation support
 
 #### 1.5.58 January 9th 2026 ####
 
@@ -79,4 +83,4 @@
 * [Added dependency-injected health checks](https://github.com/akkadotnet/Akka.Hosting/pull/659) - `WithHealthCheck<T>()` generic methods for DI-resolved health checks
 
 **Updates**
-* [Bump Akka version from 1.5.50 to 1.5.51](https://github.com/akkadotnet/akka.net/releases/tag/1.5.51)
+* [Bump Akka version from 1.5.50 to 1.5.51](https://github.com/akkadotnet/akka.net/releases/tag/1.5.51)

src/Akka.Cluster.Hosting.Tests/ClusterOptionsSpec.cs

@@ -144,7 +144,7 @@ public void ClusterOptionsConfigurationTest()
         using var stream = new MemoryStream(Encoding.UTF8.GetBytes(json));
         var jsonConfig = new ConfigurationBuilder().AddJsonStream(stream).Build();
 
-        var clusterOptions = jsonConfig.GetSection("Akka:ClusterOptions").Get<ClusterOptions>();
+        var clusterOptions = jsonConfig.GetSection("Akka:ClusterOptions").Get<ClusterOptions>()!;
         clusterOptions.SplitBrainResolver = jsonConfig.GetSection("Akka:KeepMajorityOption").Get<KeepMajorityOption>();
 
         var builder = new AkkaConfigurationBuilder(new ServiceCollection(), "")

src/Akka.Cluster.Hosting.Tests/XUnitLogger.cs

@@ -58,7 +58,7 @@ public bool IsEnabled(LogLevel logLevel)
         };
     }
 
-    public IDisposable BeginScope<TState>(TState state)
+    public IDisposable? BeginScope<TState>(TState state) where TState : notnull
     {
         throw new NotImplementedException();
     }

src/Akka.Hosting.API.Tests/verify/CoreApiSpec.ApproveCore.verified.txt

@@ -99,6 +99,10 @@ namespace Akka.Hosting
         public static Akka.Hosting.AkkaConfigurationBuilder WithHealthCheck(this Akka.Hosting.AkkaConfigurationBuilder builder, string name, Akka.Hosting.IAkkaHealthCheck healthCheck, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
         public static Akka.Hosting.AkkaConfigurationBuilder WithHealthCheck(this Akka.Hosting.AkkaConfigurationBuilder builder, string name, System.Func<Akka.Actor.ActorSystem, Akka.Hosting.ActorRegistry, System.Threading.CancellationToken, System.Threading.Tasks.Task<Microsoft.Extensions.Diagnostics.HealthChecks.HealthCheckResult>> healthCheck, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
     }
+    public static class AkkaOpenTelemetryExtensions
+    {
+        public static OpenTelemetry.Logs.OpenTelemetryLoggerOptions AddAkkaTraceCorrelation(this OpenTelemetry.Logs.OpenTelemetryLoggerOptions options) { }
+    }
     public class DeadLetterOptions
     {
         public DeadLetterOptions() { }
@@ -251,6 +255,11 @@ namespace Akka.Hosting.HealthChecks
 }
 namespace Akka.Hosting.Logging
 {
+    public sealed class AkkaTraceContextProcessor : OpenTelemetry.BaseProcessor<OpenTelemetry.Logs.LogRecord>
+    {
+        public AkkaTraceContextProcessor() { }
+        public override void OnEnd(OpenTelemetry.Logs.LogRecord data) { }
+    }
     public class LoggerFactoryLogger : Akka.Actor.ActorBase, Akka.Dispatch.IRequiresMessageQueue<Akka.Event.ILoggerMessageQueueSemantics>
     {
         protected readonly Akka.Event.ILoggingAdapter InternalLogger;
@@ -264,4 +273,4 @@ namespace Akka.Hosting.Logging
         public LoggerFactorySetup(Microsoft.Extensions.Logging.ILoggerFactory loggerFactory) { }
         public Microsoft.Extensions.Logging.ILoggerFactory LoggerFactory { get; }
     }
-}
+}

src/Akka.Hosting.API.Tests/verify/CoreApiSpec.ApproveTestKit.verified.txt

@@ -9,7 +9,8 @@ namespace Akka.Hosting.TestKit.Internals
     public class XUnitLogger : Microsoft.Extensions.Logging.ILogger
     {
         public XUnitLogger(string category, Xunit.Abstractions.ITestOutputHelper helper, Microsoft.Extensions.Logging.LogLevel logLevel) { }
-        public System.IDisposable BeginScope<TState>(TState state) { }
+        public System.IDisposable? BeginScope<TState>(TState state)
+            where TState :  notnull { }
         public bool IsEnabled(Microsoft.Extensions.Logging.LogLevel logLevel) { }
         public void Log<TState>(Microsoft.Extensions.Logging.LogLevel logLevel, Microsoft.Extensions.Logging.EventId eventId, TState state, System.Exception? exception, System.Func<TState, System.Exception?, string> formatter) { }
     }

src/Akka.Hosting.TestKit.Tests/Akka.Hosting.TestKit.Tests.csproj

@@ -9,7 +9,7 @@
     </ItemGroup>
 
     <ItemGroup>
-        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="7.0.0" />
+        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />
         <PackageReference Include="xunit" Version="$(XunitVersion)" />
         <PackageReference Include="FluentAssertions" Version="6.12.2" />

src/Akka.Hosting.TestKit/Akka.Hosting.TestKit.csproj

@@ -11,7 +11,7 @@
     <ItemGroup>
         <PackageReference Include="Akka.TestKit.Xunit2" Version="$(AkkaVersion)" />
         <PackageReference Include="Akka.Persistence.TestKit" Version="$(AkkaVersion)" />
-        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="7.0.0" />
+        <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
         <PackageReference Include="xunit" Version="$(XunitVersion)" />
         <PackageReference Include="Microsoft.Extensions.Hosting" Version="$(MicrosoftExtensionsVersion)" />
         <PackageReference Include="System.Text.Json" Version="$(SystemTextJsonVersion)" />

src/Akka.Hosting.TestKit/Internals/XUnitLogger.cs

@@ -68,7 +68,7 @@ public bool IsEnabled(LogLevel logLevel)
             };
         }
 
-        public IDisposable BeginScope<TState>(TState state) 
+        public IDisposable? BeginScope<TState>(TState state) where TState : notnull
         {
             return NullScope.Instance;
         }

src/Akka.Hosting.Tests/Akka.Hosting.Tests.csproj

@@ -8,7 +8,7 @@
     <PackageReference Include="Microsoft.Extensions.Hosting" Version="$(MicrosoftExtensionsVersion)" />
     <PackageReference Include="System.Text.Json" Version="$(SystemTextJsonVersion)" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="8.0.1" />
-    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="7.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="8.0.0" />
     <PackageReference Include="Akka.TestKit.Xunit2" Version="$(AkkaVersion)" />
     <PackageReference Include="FluentAssertions" Version="6.12.2" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />