Serilog — Setup, Sinks and Enrichers

Serilog is the most widely used structured logging library for .NET — it integrates with ASP.NET Core’s ILogger abstraction, outputs structured JSON to multiple destinations (sinks) simultaneously, and enriches every log entry with contextual properties. While ASP.NET Core’s built-in logging is functional, Serilog provides a richer feature set for production: sink variety (Seq, Application Insights, Elasticsearch, S3), enrichers (machine name, environment, process ID), and better control over output formats. Setting up Serilog is the first infrastructure task in most production ASP.NET Core projects.

Serilog Setup #

// dotnet add package Serilog.AspNetCore
// dotnet add package Serilog.Sinks.Console
// dotnet add package Serilog.Sinks.File
// dotnet add package Serilog.Enrichers.Environment
// dotnet add package Serilog.Enrichers.Process

// ── Program.cs — configure Serilog before building the host ───────────────
// Bootstrap logger for startup errors (before host builds)
Log.Logger = new LoggerConfiguration()
    .WriteTo.Console()
    .CreateBootstrapLogger();

try
{
    var builder = WebApplication.CreateBuilder(args);

    // Replace default logging with Serilog
    builder.Host.UseSerilog((context, services, config) =>
    {
        config
            // Read base settings from appsettings.json "Serilog" section
            .ReadFrom.Configuration(context.Configuration)
            .ReadFrom.Services(services)   // allows sinks to use DI services
            // Enrichers — add properties to every log entry
            .Enrich.FromLogContext()              // reads from BeginScope
            .Enrich.WithMachineName()
            .Enrich.WithEnvironmentName()
            .Enrich.WithProcessId()
            // Sinks — where logs are written
            .WriteTo.Console(
                outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} ({SourceContext}){NewLine}{Exception}")
            .WriteTo.File(
                path: "logs/blogapp-.log",
                rollingInterval: RollingInterval.Day,
                retainedFileCountLimit: 7,
                outputTemplate: "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj}{NewLine}{Exception}");
    });

    // ... register services
    var app = builder.Build();
    // ... configure pipeline
    app.Run();
}
catch (Exception ex)
{
    Log.Fatal(ex, "Application terminated unexpectedly.");
}
finally
{
    Log.CloseAndFlush();   // ensures all buffered log entries are written
}

Serilog Configuration in appsettings.json #

// ── appsettings.json Serilog section ──────────────────────────────────────
// {
//   "Serilog": {
//     "Using": ["Serilog.Sinks.Console", "Serilog.Sinks.File"],
//     "MinimumLevel": {
//       "Default": "Information",
//       "Override": {
//         "Microsoft": "Warning",
//         "Microsoft.AspNetCore": "Warning",
//         "Microsoft.EntityFrameworkCore": "Warning",
//         "BlogApp": "Debug"
//       }
//     },
//     "WriteTo": [
//       {
//         "Name": "Console",
//         "Args": {
//           "outputTemplate": "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}"
//         }
//       },
//       {
//         "Name": "File",
//         "Args": {
//           "path": "logs/blogapp-.log",
//           "rollingInterval": "Day",
//           "retainedFileCountLimit": 7
//         }
//       }
//     ],
//     "Enrich": ["FromLogContext", "WithMachineName", "WithEnvironmentName"]
//   }
// }

Common Mistakes #

Mistake 1 — Not calling Log.CloseAndFlush() (lost log entries on exit) #

❌ Wrong — last entries may be buffered and never written:

app.Run();
// Application exits — buffered entries lost!

✅ Correct — wrap in try/finally and call Log.CloseAndFlush() in finally.

Mistake 2 — Omitting .Enrich.FromLogContext() (log scopes not captured) #

❌ Wrong — without this enricher, BeginScope properties are not added to Serilog entries.

✅ Correct — always include .Enrich.FromLogContext() to capture ILogger scope properties.