Logging Configuration for .NET

Overview

This skill configures structured logging following Microsoft best practices:

• ILogger - Inject into services for category-based logging
• ILoggerFactory - Create loggers dynamically when needed
• Structured Logging - Preserve log properties for analysis
• Source Generators - High-performance compile-time logging
• Serilog Integration - Enhanced sinks and enrichers

Quick Reference

Interface	Lifetime	Use Case
ILogger<T>	Singleton	Standard service logging
ILoggerFactory	Singleton	Create loggers dynamically
ILogger	-	Non-generic (avoid in DI)

---

Logging Structure

/Infrastructure/Logging/
├── LoggerConfiguration.cs
├── LogEvents.cs           # LoggerMessage source generators
├── LogEnrichers/
│   ├── UserContextEnricher.cs
│   └── CorrelationIdEnricher.cs
└── Sinks/
    └── CustomSink.cs

---

Template: Service with ILogger

// src/{name}.application/Services/OrderService.cs
using Microsoft.Extensions.Logging;

namespace {name}.application.services;

/// <summary>
/// Services should inject ILogger<T> for category-based logging.
/// The category is automatically set to the full type name.
/// </summary>
public sealed class OrderService : IOrderService
{
    private readonly ILogger<OrderService> _logger;
    private readonly IOrderRepository _orderRepository;

    public OrderService(
        ILogger<OrderService> logger,
        IOrderRepository orderRepository)
    {
        _logger = logger;
        _orderRepository = orderRepository;
    }

    public async Task<Result<Order>> ProcessOrderAsync(
        Guid orderId,
        CancellationToken cancellationToken)
    {
        // ═══════════════════════════════════════════════════════════════
        // STRUCTURED LOGGING - Use placeholders, not string interpolation
        // ═══════════════════════════════════════════════════════════════
        _logger.LogInformation(
            "Processing order {OrderId}",
            orderId);

        try
        {
            var order = await _orderRepository.GetByIdAsync(orderId, cancellationToken);

            if (order is null)
            {
                _logger.LogWarning(
                    "Order {OrderId} not found",
                    orderId);

                return Result.Failure<Order>(OrderErrors.NotFound(orderId));
            }

            // Log with multiple properties
            _logger.LogInformation(
                "Order {OrderId} retrieved. Status: {Status}, Total: {Total}",
                orderId,
                order.Status,
                order.Total);

            return Result.Success(order);
        }
        catch (Exception ex)
        {
            // Always log exceptions with the exception parameter first
            _logger.LogError(
                ex,
                "Error processing order {OrderId}",
                orderId);

            throw;
        }
    }
}

---

Template: ILoggerFactory Usage

// src/{name}.infrastructure/Services/DynamicLoggerService.cs
using Microsoft.Extensions.Logging;

namespace {name}.infrastructure.services;

/// <summary>
/// Use ILoggerFactory when you need to create loggers dynamically.
/// Common use cases:
/// - Factory classes that create multiple types
/// - Plugin systems where type isn't known at compile time
/// - Base classes that want child-specific categories
/// </summary>
public sealed class PluginManager
{
    private readonly ILoggerFactory _loggerFactory;

    public PluginManager(ILoggerFactory loggerFactory)
    {
        _loggerFactory = loggerFactory;
    }

    public IPlugin LoadPlugin(string pluginName, Type pluginType)
    {
        // Create a logger with a dynamic category
        var logger = _loggerFactory.CreateLogger(pluginType);

        logger.LogInformation(
            "Loading plugin {PluginName} of type {PluginType}",
            pluginName,
            pluginType.Name);

        // Or with a string category
        var customLogger = _loggerFactory.CreateLogger($"Plugins.{pluginName}");

        customLogger.LogDebug(
            "Plugin {PluginName} initialized",
            pluginName);

        return CreatePlugin(pluginType, customLogger);
    }
}

---

Template: High-Performance Logging with Source Generators

// src/{name}.application/Logging/LogEvents.cs
using Microsoft.Extensions.Logging;

namespace {name}.application.logging;

/// <summary>
/// LoggerMessage source generators provide the best logging performance.
/// Benefits:
/// - Zero allocation for disabled log levels
/// - Compile-time validation of message templates
/// - Strongly typed parameters
/// </summary>
public static partial class LogEvents
{
    // ═══════════════════════════════════════════════════════════════
    // INFORMATION LEVEL
    // ═══════════════════════════════════════════════════════════════

    [LoggerMessage(
        EventId = 1000,
        Level = LogLevel.Information,
        Message = "Processing request {RequestName} with ID {RequestId}")]
    public static partial void LogRequestProcessing(
        this ILogger logger,
        string requestName,
        Guid requestId);

    [LoggerMessage(
        EventId = 1001,
        Level = LogLevel.Information,
        Message = "Request {RequestName} completed in {ElapsedMs}ms")]
    public static partial void LogRequestCompleted(
        this ILogger logger,
        string requestName,
        long elapsedMs);

    [LoggerMessage(
        EventId = 1002,
        Level = LogLevel.Information,
        Message = "User {UserId} authenticated successfully")]
    public static partial void LogUserAuthenticated(
        this ILogger logger,
        Guid userId);

    // ═══════════════════════════════════════════════════════════════
    // WARNING LEVEL
    // ═══════════════════════════════════════════════════════════════

    [LoggerMessage(
        EventId = 2000,
        Level = LogLevel.Warning,
        Message = "Slow request detected: {RequestName} took {ElapsedMs}ms")]
    public static partial void LogSlowRequest(
        this ILogger logger,
        string requestName,
        long elapsedMs);

    [LoggerMessage(
        EventId = 2001,
        Level = LogLevel.Warning,
        Message = "Cache miss for key {CacheKey}")]
    public static partial void LogCacheMiss(
        this ILogger logger,
        string cacheKey);

    [LoggerMessage(
        EventId = 2002,
        Level = LogLevel.Warning,
        Message = "Rate limit exceeded for client {ClientId}")]
    public static partial void LogRateLimitExceeded(
        this ILogger logger,
        string clientId);

    // ═══════════════════════════════════════════════════════════════
    // ERROR LEVEL
    // ═══════════════════════════════════════════════════════════════

    [LoggerMessage(
        EventId = 3000,
        Level = LogLevel.Error,
        Message = "Error processing request {RequestName}")]
    public static partial void LogRequestError(
        this ILogger logger,
        Exception exception,
        string requestName);

    [LoggerMessage(
        EventId = 3001,
        Level = LogLevel.Error,
        Message = "Database operation failed for entity {EntityType} with ID {EntityId}")]
    public static partial void LogDatabaseError(
        this ILogger logger,
        Exception exception,
        string entityType,
        Guid entityId);

    [LoggerMessage(
        EventId = 3002,
        Level = LogLevel.Error,
        Message = "External service {ServiceName} returned error: {ErrorCode}")]
    public static partial void LogExternalServiceError(
        this ILogger logger,
        string serviceName,
        string errorCode);

    // ═══════════════════════════════════════════════════════════════
    // DEBUG LEVEL
    // ═══════════════════════════════════════════════════════════════

    [LoggerMessage(
        EventId = 4000,
        Level = LogLevel.Debug,
        Message = "Executing query: {QueryName}")]
    public static partial void LogQueryExecution(
        this ILogger logger,
        string queryName);

    [LoggerMessage(
        EventId = 4001,
        Level = LogLevel.Debug,
        Message = "Cache hit for key {CacheKey}")]
    public static partial void LogCacheHit(
        this ILogger logger,
        string cacheKey);
}

Using Source Generated Logs

// src/{name}.application/Features/Orders/ProcessOrder/ProcessOrderHandler.cs
public sealed class ProcessOrderHandler : ICommandHandler<ProcessOrderCommand, Guid>
{
    private readonly ILogger<ProcessOrderHandler> _logger;

    public async Task<Result<Guid>> Handle(
        ProcessOrderCommand command,
        CancellationToken cancellationToken)
    {
        // Use extension method from LogEvents
        _logger.LogRequestProcessing("ProcessOrder", command.OrderId);

        var stopwatch = Stopwatch.StartNew();

        try
        {
            // ... process order ...

            stopwatch.Stop();
            _logger.LogRequestCompleted("ProcessOrder", stopwatch.ElapsedMilliseconds);

            return Result.Success(command.OrderId);
        }
        catch (Exception ex)
        {
            _logger.LogRequestError(ex, "ProcessOrder");
            throw;
        }
    }
}

---

Template: Serilog Configuration

// src/{name}.api/Program.cs
using Serilog;
using Serilog.Events;

var builder = WebApplication.CreateBuilder(args);

// ═══════════════════════════════════════════════════════════════
// SERILOG CONFIGURATION
// ═══════════════════════════════════════════════════════════════
Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Information()
    .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
    .MinimumLevel.Override("Microsoft.Hosting.Lifetime", LogEventLevel.Information)
    .MinimumLevel.Override("Microsoft.EntityFrameworkCore", LogEventLevel.Warning)
    .Enrich.FromLogContext()
    .Enrich.WithMachineName()
    .Enrich.WithEnvironmentName()
    .Enrich.WithProperty("Application", "MyApp")
    .WriteTo.Console(outputTemplate:
        "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}")
    .WriteTo.File(
        path: "logs/log-.txt",
        rollingInterval: RollingInterval.Day,
        retainedFileCountLimit: 30,
        outputTemplate: "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}")
    .CreateLogger();

builder.Host.UseSerilog();

// ... rest of configuration ...

var app = builder.Build();

// Request logging middleware
app.UseSerilogRequestLogging(options =>
{
    options.MessageTemplate = "HTTP {RequestMethod} {RequestPath} responded {StatusCode} in {Elapsed:0.0000}ms";
    options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
    {
        diagnosticContext.Set("RequestHost", httpContext.Request.Host.Value);
        diagnosticContext.Set("UserAgent", httpContext.Request.Headers["User-Agent"].ToString());
    };
});

---

Template: appsettings.json Logging Configuration

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information",
      "Microsoft.EntityFrameworkCore": "Warning",
      "Microsoft.EntityFrameworkCore.Database.Command": "Warning"
    }
  },
  "Serilog": {
    "Using": ["Serilog.Sinks.Console", "Serilog.Sinks.File", "Serilog.Sinks.Seq"],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning",
        "Microsoft.EntityFrameworkCore": "Warning",
        "System": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "Console",
        "Args": {
          "theme": "Serilog.Sinks.SystemConsole.Themes.AnsiConsoleTheme::Code, Serilog.Sinks.Console"
        }
      },
      {
        "Name": "File",
        "Args": {
          "path": "logs/log-.txt",
          "rollingInterval": "Day",
          "retainedFileCountLimit": 30
        }
      },
      {
        "Name": "Seq",
        "Args": {
          "serverUrl": "http://localhost:5341"
        }
      }
    ],
    "Enrich": ["FromLogContext", "WithMachineName", "WithEnvironmentName"],
    "Properties": {
      "Application": "MyApp"
    }
  }
}

---

Template: Correlation ID Enricher

// src/{name}.infrastructure/Logging/CorrelationIdEnricher.cs
using Serilog.Core;
using Serilog.Events;

namespace {name}.infrastructure.logging;

/// <summary>
/// Enriches all logs with a correlation ID for request tracing.
/// </summary>
public sealed class CorrelationIdEnricher : ILogEventEnricher
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private const string CorrelationIdHeader = "X-Correlation-ID";
    private const string CorrelationIdProperty = "CorrelationId";

    public CorrelationIdEnricher(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
    {
        var correlationId = GetCorrelationId();

        var property = propertyFactory.CreateProperty(CorrelationIdProperty, correlationId);
        logEvent.AddPropertyIfAbsent(property);
    }

    private string GetCorrelationId()
    {
        var context = _httpContextAccessor.HttpContext;

        if (context is null)
        {
            return Guid.NewGuid().ToString();
        }

        // Try to get from header first
        if (context.Request.Headers.TryGetValue(CorrelationIdHeader, out var headerValue))
        {
            return headerValue.ToString();
        }

        // Generate and store in context
        if (!context.Items.ContainsKey(CorrelationIdProperty))
        {
            context.Items[CorrelationIdProperty] = Guid.NewGuid().ToString();
        }

        return context.Items[CorrelationIdProperty]!.ToString()!;
    }
}

---

Template: User Context Enricher

// src/{name}.infrastructure/Logging/UserContextEnricher.cs
using Serilog.Core;
using Serilog.Events;

namespace {name}.infrastructure.logging;

/// <summary>
/// Enriches logs with current user information.
/// </summary>
public sealed class UserContextEnricher : ILogEventEnricher
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public UserContextEnricher(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
    {
        var context = _httpContextAccessor.HttpContext;

        if (context?.User.Identity?.IsAuthenticated != true)
        {
            return;
        }

        var userId = context.User.FindFirst("sub")?.Value
                  ?? context.User.FindFirst(ClaimTypes.NameIdentifier)?.Value;

        if (!string.IsNullOrEmpty(userId))
        {
            var property = propertyFactory.CreateProperty("UserId", userId);
            logEvent.AddPropertyIfAbsent(property);
        }

        var userName = context.User.Identity.Name;
        if (!string.IsNullOrEmpty(userName))
        {
            var property = propertyFactory.CreateProperty("UserName", userName);
            logEvent.AddPropertyIfAbsent(property);
        }
    }
}

---

Template: Dependency Injection Registration

// src/{name}.infrastructure/DependencyInjection.cs
using Microsoft.Extensions.DependencyInjection;
using Serilog;

namespace {name}.infrastructure;

public static class DependencyInjection
{
    public static IServiceCollection AddInfrastructure(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        // ═══════════════════════════════════════════════════════════════
        // LOGGING CONFIGURATION
        // ═══════════════════════════════════════════════════════════════
        services.AddLogging(loggingBuilder =>
        {
            loggingBuilder.ClearProviders();
            loggingBuilder.AddSerilog(dispose: true);
        });

        // Register enrichers
        services.AddSingleton<CorrelationIdEnricher>();
        services.AddSingleton<UserContextEnricher>();

        return services;
    }
}

---

Template: Scoped Logging with BeginScope

// src/{name}.application/Features/Orders/ProcessOrder/ProcessOrderHandler.cs
public sealed class ProcessOrderHandler : ICommandHandler<ProcessOrderCommand, Guid>
{
    private readonly ILogger<ProcessOrderHandler> _logger;

    public async Task<Result<Guid>> Handle(
        ProcessOrderCommand command,
        CancellationToken cancellationToken)
    {
        // ═══════════════════════════════════════════════════════════════
        // SCOPED LOGGING - All logs within scope include these properties
        // ═══════════════════════════════════════════════════════════════
        using (_logger.BeginScope(new Dictionary<string, object>
        {
            ["OrderId"] = command.OrderId,
            ["UserId"] = command.UserId,
            ["Operation"] = "ProcessOrder"
        }))
        {
            _logger.LogInformation("Starting order processing");

            // All logs within this scope automatically include OrderId, UserId, Operation
            await ValidateOrder(command);
            await CalculateTotals(command);
            await ProcessPayment(command);

            _logger.LogInformation("Order processing completed");
        }

        return Result.Success(command.OrderId);
    }
}

---

Log Levels Guide

Level	Use For
Trace	Detailed debugging (not in production)
Debug	Development debugging
Information	General flow, important events
Warning	Unexpected but handled events
Error	Failures requiring attention
Critical	System failures requiring immediate action

---

Critical Rules

1. Always use ILogger - Category-based logging for traceability
2. Use structured logging - {Property} placeholders, not string interpolation
3. Include context - Add relevant IDs and data to logs
4. Log at appropriate levels - Don't use Error for normal flow
5. Use source generators - For high-performance hot paths
6. Don't log sensitive data - No passwords, tokens, or PII
7. Include correlation IDs - For request tracing across services
8. Configure per-namespace levels - Reduce noise from frameworks
9. Use scopes for operations - Group related logs together
10. Always pass exceptions first - LogError(ex, "Message") not in message

---

Anti-Patterns to Avoid

// ❌ WRONG: String interpolation
_logger.LogInformation($"Processing order {orderId}");

// ✅ CORRECT: Structured logging with placeholders
_logger.LogInformation("Processing order {OrderId}", orderId);

// ❌ WRONG: Logging sensitive data
_logger.LogInformation("User {Email} logged in with password {Password}", email, password);

// ✅ CORRECT: Redact sensitive data
_logger.LogInformation("User {Email} logged in", email);

// ❌ WRONG: Exception in message
_logger.LogError($"Error: {exception.Message}");

// ✅ CORRECT: Exception as first parameter
_logger.LogError(exception, "Error processing request");

// ❌ WRONG: Injecting ILoggerFactory when ILogger<T> suffices
public class OrderService
{
    private readonly ILogger _logger;
    public OrderService(ILoggerFactory factory)
    {
        _logger = factory.CreateLogger<OrderService>();  // Unnecessary!
    }
}

// ✅ CORRECT: Inject ILogger<T> directly
public class OrderService
{
    private readonly ILogger<OrderService> _logger;
    public OrderService(ILogger<OrderService> logger)
    {
        _logger = logger;
    }
}

// ❌ WRONG: Checking log level unnecessarily (with source generators)
if (_logger.IsEnabled(LogLevel.Debug))
{
    _logger.LogDebug("Value: {Value}", expensiveOperation());
}

// ✅ CORRECT: Source generators handle this automatically
_logger.LogQueryExecution("GetOrderById");  // No-op if Debug disabled

---

Packages Required

# Core logging
dotnet add package Microsoft.Extensions.Logging

# Serilog (recommended)
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

# Optional: Centralized logging
dotnet add package Serilog.Sinks.Seq          # Seq server
dotnet add package Serilog.Sinks.Elasticsearch # Elasticsearch
dotnet add package Serilog.Sinks.ApplicationInsights # Azure

---

Related Skills

• 10-dotnet-pipeline-behaviors - Logging behavior for all requests
• 17-dotnet-health-checks - Application monitoring
• 01-dotnet-clean-architecture - Overall architecture