Logging in .NET

Structured Logging

When logging and using a provider that supports structured/semantic logging, we should provide parameters the following way:

// GOOD
_logger.LogInformation("User {userId} logged in", userId);

// BAD
_logger.logInformation($"User {userId} logged in");

The first way stores both the value of the parameter (the actual user identifier) and the name of this parameter. In the second approach, the name is lost, so we are not able to filter based on the named parameter (userId).

Log Storage

Structured logs can be stored in systems like:

• Elasticsearch
• Seq

Serilog

Using Serilog:

1. Install NuGet packages:

   dotnet add package Serilog.Sinks.Console # Console sink
   dotnet add package Serilog.Settings.Configuration # allows reading settings from a file
   dotnet add package Serilog.Extensions.Logging # DI

2. Use Serilog with DI

   var host = Host.CreateDefaultBuilder(args)
   .ConfigureServices((host, services) =>
   {
       services.AddLogging(builder =>
       {
           var logger = new LoggerConfiguration()
               .ReadFrom.Configuration(host.Configuration) // Serilog.Settings.Configuration
               .CreateLogger();
   
           builder.ClearProviders(); // removes the default logger
           builder.AddSerilog(logger);
       });
   
       // Other services...
   })
   .Build();

3. Configure

   In appsettings.json:

   {
       "Serilog": {
           "Using":  [ "Serilog.Sinks.Console" ],
           "MinimumLevel": "Debug",
           "WriteTo": [ "Console" ]
       }
   }

   More information can be found here.

Usage without Dependency Injection

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

try
{
    // Run the app...
}
catch(Exception e)
{
    Log.Fatal(e, "Host terminated unexpectedly");
}
finally
{
    Log.CloseAndFlush();
}

Logging to files with Serilog

public static void AddLogging(this IServiceCollection services, AppConfiguration appConfiguration)
{
    services.AddLogging(services, builder => {
        builder.SetMinimumLevel(appConfiguration.LogLevel);
        builder.AddSerilog(builder, GetSerilogLogger(appConfiguration), true);
    });
}

private static Serilog.Core.Logger GetSerilogLogger(AppConfiguration appConfiguration)
{
    var configuration = Serilog.ConsoleLoggerConfigurationExtensions.Console(
        new Serilog.LoggerConfiguration()
            .MinimumLevel.Verbose()
            .WriteTo);

    if(appConfiguration.LogToFile)
    {
        Serilog.FileLoggerConfigurationExtensions.File(configuration.WriteTo, appConfiguration.LogPath);
    }

    return configuration.CreateLogger();
}