Serilog.Extensions.Logging

A Serilog provider for Microsoft.Extensions.Logging, the logging subsystem used by ASP.NET Core.

ASP.NET Core Instructions

ASP.NET Core applications should prefer Serilog.AspNetCore and UseSerilog() instead.

Non-web .NET Core Instructions

Non-web .NET Core applications should prefer Serilog.Extensions.Hosting and UseSerilog() instead.

.NET Core 1.0, 1.1 and Default Provider Integration

The package implements AddSerilog() on ILoggingBuilder and ILoggerFactory to enable the Serilog provider under the default Microsoft.Extensions.Logging implementation.

First, install the Serilog.Extensions.Logging NuGet package into your web or console app. You will need a way to view the log messages - Serilog.Sinks.Console writes these to the console.

Install-Package Serilog.Extensions.Logging -DependencyVersion Highest
Install-Package Serilog.Sinks.Console

Next, in your application's Startup method, configure Serilog first:

using Serilog;

public class Startup
{
  public Startup(IHostingEnvironment env)
  {
    Log.Logger = new LoggerConfiguration()
      .Enrich.FromLogContext()
      .WriteTo.Console()
      .CreateLogger();
      
    // Other startup code

Finally, for .NET Core 2.0+, in your Startup class's Configure() method, remove the existing logger configuration entries and call AddSerilog() on the provided loggingBuilder.

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddLogging(loggingBuilder =>
      	loggingBuilder.AddSerilog(dispose: true));
      
      // Other services ...
  }

For .NET Core 1.0 or 1.1, in your Startup class's Configure() method, remove the existing logger configuration entries and call AddSerilog() on the provided loggerFactory.

  public void Configure(IApplicationBuilder app,
                        IHostingEnvironment env,
                        ILoggerFactory loggerfactory,
                        IApplicationLifetime appLifetime)
  {
      loggerfactory.AddSerilog();
      
      // Ensure any buffered events are sent at shutdown
      appLifetime.ApplicationStopped.Register(Log.CloseAndFlush);

That's it! With the level bumped up a little you should see log output like:

[22:14:44.646 DBG] RouteCollection.RouteAsync
	Routes: 
		Microsoft.AspNet.Mvc.Routing.AttributeRoute
		{controller=Home}/{action=Index}/{id?}
	Handled? True
[22:14:44.647 DBG] RouterMiddleware.Invoke
	Handled? True
[22:14:45.706 DBG] /lib/jquery/jquery.js not modified
[22:14:45.706 DBG] /css/site.css not modified
[22:14:45.741 DBG] Handled. Status code: 304 File: /css/site.css

Notes on Log Scopes

Microsoft.Extensions.Logging provides the BeginScope API, which can be used to add arbitrary properties to log events within a certain region of code. The API comes in two forms:

1. The method: IDisposable BeginScope<TState>(TState state)
2. The extension method: IDisposable BeginScope(this ILogger logger, string messageFormat, params object[] args)

Using the extension method will add a Scope property to your log events. This is most useful for adding simple "scope strings" to your events, as in the following code:

using (_logger.BeginScope("Transaction")) {
    _logger.LogInformation("Beginning...");
    _logger.LogInformation("Completed in {DurationMs}ms...", 30);
}
// Example JSON output:
// {"@t":"2020-10-29T19:05:56.4126822Z","@m":"Beginning...","@i":"f6a328e9","SourceContext":"SomeNamespace.SomeService","Scope":["Transaction"]}
// {"@t":"2020-10-29T19:05:56.4176816Z","@m":"Completed in 30ms...","@i":"51812baa","DurationMs":30,"SourceContext":"SomeNamespace.SomeService","Scope":["Transaction"]}

If you simply want to add a "bag" of additional properties to your log events, however, this extension method approach can be overly verbose. For example, to add TransactionId and ResponseJson properties to your log events, you would have to do something like the following:

// WRONG! Prefer the dictionary approach below instead
using (_logger.BeginScope("TransactionId: {TransactionId}, ResponseJson: {ResponseJson}", 12345, jsonString)) {
    _logger.LogInformation("Completed in {DurationMs}ms...", 30);
}
// Example JSON output:
// {
//	"@t":"2020-10-29T19:05:56.4176816Z",
//	"@m":"Completed in 30ms...",
//	"@i":"51812baa",
//	"DurationMs":30,
//	"SourceContext":"SomeNamespace.SomeService",
//	"TransactionId": 12345,
//	"ResponseJson": "{ \"Key1\": \"Value1\", \"Key2\": \"Value2\" }",
//	"Scope":["TransactionId: 12345, ResponseJson: { \"Key1\": \"Value1\", \"Key2\": \"Value2\" }"]
// }

Not only does this add the unnecessary Scope property to your event, but it also duplicates serialized values between Scope and the intended properties, as you can see here with ResponseJson. If this were "real" JSON like an API response, then a potentially very large block of text would be duplicated within your log event! Moreover, the template string within BeginScope is rather arbitrary when all you want to do is add a bag of properties, and you start mixing enriching concerns with formatting concerns.

A far better alternative is to use the BeginScope<TState>(TState state) method. If you provide any IEnumerable<KeyValuePair<string, object>> to this method, then Serilog will output the key/value pairs as structured properties without the Scope property, as in this example:

var scopeProps = new Dictionary<string, object> {
    { "TransactionId", 12345 },
    { "ResponseJson", jsonString },
};
using (_logger.BeginScope(scopeProps) {
    _logger.LogInformation("Transaction completed in {DurationMs}ms...", 30);
}
// Example JSON output:
// {
//	"@t":"2020-10-29T19:05:56.4176816Z",
//	"@m":"Completed in 30ms...",
//	"@i":"51812baa",
//	"DurationMs":30,
//	"SourceContext":"SomeNamespace.SomeService",
//	"TransactionId": 12345,
//	"ResponseJson": "{ \"Key1\": \"Value1\", \"Key2\": \"Value2\" }"
// }

Credits

This package evolved from an earlier package Microsoft.Framework.Logging.Serilog provided by the ASP.NET team.