net6.0 Serilog example

This is a sample project showing Serilog configured in the default .NET 6 web application template.

To show how everything fits together, the sample includes:

• Support for .NET 6's ILogger<T> and WebApplicationBuilder
• Namespace-specific logging levels to suppress noise from the framework
• JSON configuration
• Clean, themed console output
• Local logging to a rolling file
• Centralized structured logging with Seq
• Streamlined HTTP request logging
• Filtering out of noisy events using Serilog.Expressions
• Exception logging
• Fallback/fail-safe bootstrap logger
• Proper flushing of logs at exit

The code is not commented, so that the structure is easier to compare with the default template. If you're keen to understand the trade-offs and reasoning behind the choices made here, there's some commentary on each section in Setting up from scratch below.

Trying it out

You'll need the .NET 6.0 SDK or later to run the sample. Check the version you have installed with:

dotnet --version

After checking out this repository or downloading a zip file of the source code, you can run the project with:

dotnet run

Some URLs will be printed to the terminal: open them in a browser to see request logging in action.

• / — should show "Hello, world!" and respond successfully
• /oops — throws an exception, which will be logged

To see structured log output, start a temporary local Seq instance with:

docker run --rm -it -e ACCEPT_EULA=y -p 5341:80 datalust/seq

and open http://localhost:5341 in your browser (for Windows users, there's also an MSI at https://datalust.co/download).

Setting up from scratch

You can freely copy code from this project to your own applications. If you'd like to set up from scratch, and skip any steps that aren't relevant to you, try following the steps below.

1. Create the project using the web template

mkdir dotnet6-serilog-example
cd dotnet6-serilog-example
dotnet new web

2. Install Serilog packages

dotnet add package serilog.aspnetcore
dotnet add package serilog.sinks.seq
dotnet add package serilog.expressions

3. Initialize Serilog at the start of Program.cs

Its important that logging is initialized as early as possible, so that errors that might prevent your app from starting are logged.

At the very top of Program.cs:

using Serilog;

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

Log.Information("Starting up");

CreateBootstrapLogger() sets up Serilog so that the initial logger configuration (which writes only to Console), can be swapped out later in the initialization process, once the web hosting infrastructure is available.

4. Wrap the rest of Program.cs in try/catch/finally

Configuration of the web application in Program.cs can now be enclosed in a try block.

try
{
    // <snip>
}
catch (Exception ex)
{
    Log.Fatal(ex, "Unhandled exception");
}
finally
{
    Log.Information("Shut down complete");
    Log.CloseAndFlush();
}

The catch block will log any exceptions thrown during start-up.

The Log.CloseAndFlush() in the finally block ensures that any queued log events will be properly recorded when the program exits.

5. Wire Serilog into the WebApplicationBuilder

    builder.Host.UseSerilog((ctx, lc) => lc
        .WriteTo.Console()
        .ReadFrom.Configuration(ctx.Configuration));

6. Replace logging configuration in appsettings.json

In appsettings.json, remove "Logging" and add "Serilog".

The complete JSON configuration from the example is:

{
  "Serilog": {
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning",
        "Microsoft.Hosting.Lifetime": "Information"
      }
    },
    "Filter": [
      {
        "Name": "ByExcluding",
        "Args": {
          "expression": "@mt = 'An unhandled exception has occurred while executing the request.'"
        }
      }
    ],
    "WriteTo": [
      {
        "Name": "File",
        "Args": { "path":  "./logs/log-.txt", "rollingInterval": "Day" }
      },
      {
        "Name": "Seq",
        "Args": { "serverUrl":  "http://localhost:5341" }
      }
    ]
  },
  "AllowedHosts": "*"
}

Remove all "Logging" configuration from appsettings.Development.json. (During development, you should normally use the same logging level as you use in production; if you can't find problems using the production logs in development, you'll have an even harder time finding problems in the real production environment.)

7. Add Serilog's request logging middleware

By default, the ASP.NET Core framework logs multiple information-level events per request.

Serilog's request logging streamlines this, into a single message per request, including path, method, timings, status code, and exception.

    app.UseSerilogRequestLogging();

Writing log events

This setup enables both Serilog's static Log class, as you see used in the example above, and Microsoft.Extensions.Logging's ILogger<T>, which can be consumed through dependency injection into controllers and other components.

Viewing structured logs

If you're running a local Seq instance, you can now view the structured properties attached to your application logs in the Seq UI:

Getting help and advice

Ask your question on Stack Overflow and tag it with serilog.