Serilog.AspNetCore

Serilog logging for ASP.NET Core. This package routes ASP.NET Core log messages through Serilog, so you can get information about ASP.NET's internal operations written to the same Serilog sinks as your application events.

With Serilog.AspNetCore installed and configured, you can write log messages directly through Serilog or any ILogger interface injected by ASP.NET. All loggers will use the same underlying implementation, levels, and destinations.

Versioning: This package tracks the versioning and target framework support of its Microsoft.Extensions.Hosting dependency. Most users should choose the version of Serilog.AspNetCore that matches their application's target framework. I.e. if you're targeting .NET 7.x, choose a 7.x version of Serilog.AspNetCore. If you're targeting .NET 8.x, choose an 8.x Serilog.AspNetCore version, and so on.

Instructions

First, install the Serilog.AspNetCore NuGet package into your app.

dotnet add package Serilog.AspNetCore

Next, in your application's Program.cs file, configure Serilog first. A try/catch block will ensure any configuration issues are appropriately logged:

using Serilog;

Log.Logger = new LoggerConfiguration()
    .WriteTo.Console()
    .CreateLogger();

try
{
    Log.Information("Starting web application");

    var builder = WebApplication.CreateBuilder(args);
    builder.Services.AddSerilog(); // <-- Add this line
    
    var app = builder.Build();
    app.MapGet("/", () => "Hello World!");

    app.Run();
}
catch (Exception ex)
{
    Log.Fatal(ex, "Application terminated unexpectedly");
}
finally
{
    Log.CloseAndFlush();
}

The builder.Services.AddSerilog() call will redirect all log events through your Serilog pipeline.

Finally, clean up by removing the remaining configuration for the default logger, including the "Logging" section from appsettings.*.json files (this can be replaced with Serilog configuration as shown in the Sample project, if required).

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

[12:01:43 INF] Starting web application
[12:01:44 INF] Now listening on: http://localhost:5000
[12:01:44 INF] Application started. Press Ctrl+C to shut down.
[12:01:44 INF] Hosting environment: Development
[12:01:44 INF] Content root path: serilog-aspnetcore/samples/Sample
[12:01:47 WRN] Failed to determine the https port for redirect.
[12:01:47 INF] Hello, world!
[12:01:47 INF] HTTP GET / responded 200 in 95.0581 ms

Tip: to see Serilog output in the Visual Studio output window when running under IIS, either select ASP.NET Core Web Server from the Show output from drop-down list, or replace WriteTo.Console() in the logger configuration with WriteTo.Debug().

A more complete example, including appsettings.json configuration, can be found in the sample project here.

Request logging

The package includes middleware for smarter HTTP request logging. The default request logging implemented by ASP.NET Core is noisy, with multiple events emitted per request. The included middleware condenses these into a single event that carries method, path, status code, and timing information.

As text, this has a format like:

[16:05:54 INF] HTTP GET / responded 200 in 227.3253 ms

Or as JSON:

{
  "@t": "2019-06-26T06:05:54.6881162Z",
  "@mt": "HTTP {RequestMethod} {RequestPath} responded {StatusCode} in {Elapsed:0.0000} ms",
  "@r": ["224.5185"],
  "RequestMethod": "GET",
  "RequestPath": "/",
  "StatusCode": 200,
  "Elapsed": 224.5185,
  "RequestId": "0HLNPVG1HI42T:00000001",
  "CorrelationId": null,
  "ConnectionId": "0HLNPVG1HI42T"
}

To enable the middleware, first change the minimum level for the noisy ASP.NET Core log sources to Warning in your logger configuration or appsettings.json file:

            .MinimumLevel.Override("Microsoft.AspNetCore.Hosting", LogEventLevel.Warning)
            .MinimumLevel.Override("Microsoft.AspNetCore.Mvc", LogEventLevel.Warning)
            .MinimumLevel.Override("Microsoft.AspNetCore.Routing", LogEventLevel.Warning)

Tip: add {SourceContext} to your console logger's output template to see the names of loggers; this can help track down the source of a noisy log event to suppress.

Then, in your application's Program.cs, add the middleware with UseSerilogRequestLogging():

    var app = builder.Build();

    app.UseSerilogRequestLogging(); // <-- Add this line

    // Other app configuration

It's important that the UseSerilogRequestLogging() call appears before handlers such as MVC. The middleware will not time or log components that appear before it in the pipeline. (This can be utilized to exclude noisy handlers from logging, such as UseStaticFiles(), by placing UseSerilogRequestLogging() after them.)

During request processing, additional properties can be attached to the completion event using IDiagnosticContext.Set():

    public class HomeController : Controller
    {
        readonly IDiagnosticContext _diagnosticContext;

        public HomeController(IDiagnosticContext diagnosticContext)
        {
            _diagnosticContext = diagnosticContext ??
                throw new ArgumentNullException(nameof(diagnosticContext));
        }

        public IActionResult Index()
        {
            // The request completion event will carry this property
            _diagnosticContext.Set("CatalogLoadTime", 1423);

            return View();
        }

This pattern has the advantage of reducing the number of log events that need to be constructed, transmitted, and stored per HTTP request. Having many properties on the same event can also make correlation of request details and other data easier.

The following request information will be added as properties by default:

• RequestMethod
• RequestPath
• StatusCode
• Elapsed

You can modify the message template used for request completion events, add additional properties, or change the event level, using the options callback on UseSerilogRequestLogging():

app.UseSerilogRequestLogging(options =>
{
    // Customize the message template
    options.MessageTemplate = "Handled {RequestPath}";
    
    // Emit debug-level events instead of the defaults
    options.GetLevel = (httpContext, elapsed, ex) => LogEventLevel.Debug;
    
    // Attach additional properties to the request completion event
    options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
    {
        diagnosticContext.Set("RequestHost", httpContext.Request.Host.Value);
        diagnosticContext.Set("RequestScheme", httpContext.Request.Scheme);
    };
});

Two-stage initialization

The example at the top of this page shows how to configure Serilog immediately when the application starts. This has the benefit of catching and reporting exceptions thrown during set-up of the ASP.NET Core host.

The downside of initializing Serilog first is that services from the ASP.NET Core host, including the appsettings.json configuration and dependency injection, aren't available yet.

To address this, Serilog supports two-stage initialization. An initial "bootstrap" logger is configured immediately when the program starts, and this is replaced by the fully-configured logger once the host has loaded.

To use this technique, first replace the initial CreateLogger() call with CreateBootstrapLogger():

using Serilog;
using Serilog.Events;

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
    .Enrich.FromLogContext()
    .WriteTo.Console()
    .CreateBootstrapLogger(); // <-- Change this line!

Then, pass a callback to AddSerilog() that creates the final logger:

builder.Services.AddSerilog((services, lc) => lc
    .ReadFrom.Configuration(builder.Configuration)
    .ReadFrom.Services(services)
    .Enrich.FromLogContext()
    .WriteTo.Console());

It's important to note that the final logger completely replaces the bootstrap logger: if you want both to log to the console, for instance, you'll need to specify WriteTo.Console() in both places, as the example shows.

Consuming appsettings.json configuration

Using two-stage initialization, insert the ReadFrom.Configuration(builder.Configuration) call shown in the example above. The JSON configuration syntax is documented in the Serilog.Settings.Configuration README.

Injecting services into enrichers and sinks

Using two-stage initialization, insert the ReadFrom.Services(services) call shown in the example above. The ReadFrom.Services() call will configure the logging pipeline with any registered implementations of the following services:

• IDestructuringPolicy
• ILogEventEnricher
• ILogEventFilter
• ILogEventSink
• LoggingLevelSwitch

JSON output

The Console(), Debug(), and File() sinks all support JSON-formatted output natively, via the included Serilog.Formatting.Compact package.

To write newline-delimited JSON, pass a CompactJsonFormatter or RenderedCompactJsonFormatter to the sink configuration method:

    .WriteTo.Console(new RenderedCompactJsonFormatter())

Writing to the Azure Diagnostics Log Stream

The Azure Diagnostic Log Stream ships events from any files in the D:\home\LogFiles\ folder. To enable this for your app, add a file sink to your LoggerConfiguration, taking care to set the shared and flushToDiskInterval parameters:

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Debug()
    .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
    .Enrich.FromLogContext()
    .WriteTo.Console()
    // Add this line:
    .WriteTo.File(
       System.IO.Path.Combine(Environment.GetEnvironmentVariable("HOME"), "LogFiles", "Application", "diagnostics.txt"),
       rollingInterval: RollingInterval.Day,
       fileSizeLimitBytes: 10 * 1024 * 1024,
       retainedFileCountLimit: 2,
       rollOnFileSizeLimit: true,
       shared: true,
       flushToDiskInterval: TimeSpan.FromSeconds(1))
    .CreateLogger();

Pushing properties to the ILogger<T>

If you want to add extra properties to all log events in a specific part of your code, you can add them to the ILogger<T> in Microsoft.Extensions.Logging with the following code. For this code to work, make sure you have added the .Enrich.FromLogContext() to the .UseSerilog(...) statement, as specified in the samples above.

// Microsoft.Extensions.Logging ILogger<T>
// Yes, it's required to use a dictionary. See https://nblumhardt.com/2016/11/ilogger-beginscope/
using (logger.BeginScope(new Dictionary<string, object>
{
    ["UserId"] = "svrooij",
    ["OperationType"] = "update",
}))
{
   // UserId and OperationType are set for all logging events in these brackets
}

The code above results in the same outcome as if you would push properties in the LogContext in Serilog. More details can be found in https://github.com/serilog/serilog/wiki/Enrichment#the-logcontext.

// Serilog LogContext
using (LogContext.PushProperty("UserId", "svrooij"))
using (LogContext.PushProperty("OperationType", "update"))
{
    // UserId and OperationType are set for all logging events in these brackets
}