Using Serilog for Akka.NET Logging

Setup

Install the package Akka.Logger.Serilog via nuget to utilize Serilog, this will also install the required Serilog package dependencies.

PM> Install-Package Akka.Logger.Serilog

ASP.NET Core

If you are using Akka.NET in an ASP.NET Core application, follow the Serilog guide to setup a logger injection. Akka.NET also works with Serilog configured using two-stage initialization.

It is important to remember that logging level is first controlled by a Serilog sink, and only then by Akka.NET, as described in this document:

Logger vs. sink minimums - it is important to realize that the logging level can only be raised for sinks, not lowered. So, if the logger's MinimumLevel is set to Information then a sink with Debug as its specified level will still only see Information level events.

Thus, if Akka.NET log level is DEBUG, but a Serilog sink log level is INFO, all debug messages from Akka will be filtered out. You can set the default logging level on host startup:

public static IHostBuilder CreateHostBuilder(string[] args) => Host.CreateDefaultBuilder(args)
        .UseSerilog((hostingContext, services, loggerConfiguration) => 
           (Environment.GetEnvironmentVariable("MY_AKKA_APP__DEFAULT_LOG_LEVEL") switch
            {
                "INFO" => loggerConfiguration.MinimumLevel.Information(),
                "WARN" => loggerConfiguration.MinimumLevel.Warning(),
                "ERROR" => loggerConfiguration.MinimumLevel.Error(),
                "DEBUG" => loggerConfiguration.MinimumLevel.Debug(),
                _ => loggerConfiguration.MinimumLevel.Information()
            })
            .WriteTo.Console()
            .ReadFrom.Services(services)
            .Enrich.FromLogContext()
            .EnrichWithCommonProperties(...)
            ... // continue logger configuration);

Serilog.Log.Logger will be initialized during host bootstrap and Akka.NET will use the final configured logger.

Example

The following example uses Serilog's Console sink available via nuget, there are wide range of other sinks available depending on your needs, for example a rolling log file sink. See serilog's documentation for details on these.

PM> Install-Package Serilog.Sinks.Console

Next, you'll need to configure the global Log.Logger and also specify to use the logger in the config when creating the system, for example like this:

var logger = new LoggerConfiguration()
    .WriteTo.Console()
    .MinimumLevel.Information()
    .CreateLogger();

Serilog.Log.Logger = logger;

var system = ActorSystem.Create("my-test-system", "akka { loglevel=INFO,  loggers=[\"Akka.Logger.Serilog.SerilogLogger, Akka.Logger.Serilog\"]}");

Logging

To log inside an actor, using the normal string.Format() syntax, get the logger and log:

var log = Context.GetLogger();
...
log.Info("The value is {0}", counter);

Or alternatively

var log = Context.GetLogger();
...
log.Info("The value is {Counter}", counter);

Enabling Semantic Logging in Akka.NET v1.5+

In order for logging statements like below to be parsed correctly:

var log = Context.GetLogger();
...
log.Info("The value is {Counter}", counter);

You need to enable the Akka.Logger.Serilog.SerilogLogMessageFormatter across your entire ActorSystem - this will replace Akka.NET's default ILogMessageFormatter with Serilog's.

You can accomplish this by setting the akka.logger-formatter setting like below:

akka.logger-formatter="Akka.Logger.Serilog.SerilogLogMessageFormatter, Akka.Logger.Serilog"

Extensions for Akka.NET v1.4 and Older

![IMPORTANT] This methodology is obsolete as of Akka.NET v1.5, but we're leaving it documented for legacy purposes.

The package Akka.Logger.Serilog also includes the extension method ForContext() for ILoggingAdapter (the object returned by Context.GetLogger()). This is analogous to Serilog's ForContext() but instead of returning a Serilog ILogger it returns an Akka.NET ILoggingAdapter. This instance acts as contextual logger that will attach a property to all events logged through it.

However, in order to use it, the parent ILoggingAdapter must be constructed through another included generic extension method for GetLogger(). For example,

using Akka.Logger.Serilog;
...
private readonly ILoggingAdapter _logger = Context.GetLogger<SerilogLoggingAdapter>();
...
private void ProcessMessage(string correlationId)
{
    var contextLogger = _logger.ForContext("CorrelationId", correlationId);
    contextLogger.Info("Processing message");
}

If the configured output template is, for example, "[{CorrelationId}] {Message}{NewLine}", and the parameter correlationId is "1234" then the resulting log would contain the line [1234] Processing message.

// configure sink with an output template
var logger = new LoggerConfiguration()
    .WriteTo.Console(outputTemplate: "[{CorrelationId}] {Message}{NewLine}")
    .MinimumLevel.Information()
    .CreateLogger();

Formatting OutputTemplate

There are few properties that one can use in their OutputTemplate for logger configuration:

  • ActorPath - contains the current actor's path.
  • LogSource - also contains ActorPath, however it can also have other values such as:
    • <TypeName> (<ActorSystemName>)
    • <string> (<ActorSystemName>)
  • Thread - thread id on which given log action was executed.

Example OutputTemplate

[{Timestamp:yyyy-MM-dd HH:mm:ss.fff} {Level:u3}] [{ActorPath}] [{SourceContext}] {Message}{NewLine}{Exception}

HOCON Configuration

In order to be able to change log level without the need to recompile, we need to employ some sort of application configuration. To use Serilog via HOCON configuration, add the following to the HOCON of the project.

akka { 
    loglevel=INFO,
    loggers=["Akka.Logger.Serilog.SerilogLogger, Akka.Logger.Serilog"]
    logger-formatter="Akka.Logger.Serilog.SerilogLogMessageFormatter, Akka.Logger.Serilog"
}

The code can then be updated as follows removing the inline HOCON from the actor system creation code. Note in the following example, if a minimum level is not specified, Information level events and higher will be processed. Please read the documentation for Serilog configuration for more details on this. It is also possible to move serilog configuration to the application configuration, for example if using a rolling log file sink, again, browsing the serilog documentation is the best place for details on that feature. 

var logger = new LoggerConfiguration()
                .WriteTo.Console()
                .MinimumLevel.Information()
                .CreateLogger();

Serilog.Log.Logger = logger;

var system = ActorSystem.Create("my-test-system");