logging

Serilog Structured Logging

Setup

// Program.cs
Log.Logger = new LoggerConfiguration()
    .ReadFrom.Configuration(builder.Configuration)
    .Enrich.FromLogContext()
    .Enrich.WithMachineName()
    .Enrich.WithEnvironmentName()
    .Enrich.WithCorrelationId()
    .CreateLogger();

builder.Host.UseSerilog();

// Request logging middleware
app.UseSerilogRequestLogging(options =>
{
    options.EnrichDiagnosticContext = (diagnosticContext, httpContext) =>
    {
        diagnosticContext.Set("UserId", httpContext.User.FindFirst(ClaimTypes.NameIdentifier)?.Value);
        diagnosticContext.Set("ClientIp", httpContext.Connection.RemoteIpAddress);
    };
});

Configuration (appsettings.json)

{
  "Serilog": {
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft.AspNetCore": "Warning",
        "Microsoft.EntityFrameworkCore": "Warning",
        "System": "Warning"
      }
    },
    "WriteTo": [
      { "Name": "Console" },
      {
        "Name": "File",
        "Args": {
          "path": "logs/log-.txt",
          "rollingInterval": "Day",
          "retainedFileCountLimit": 7
        }
      }
    ]
  }
}

Structured Logging Best Practices

// CORRECT - Structured with named properties
_logger.LogInformation("User {UserId} created order {OrderId} for {Amount:C}", 
    userId, orderId, amount);

// WRONG - String interpolation (loses structure)
_logger.LogInformation($"User {userId} created order {orderId} for {amount:C}");

// CORRECT - Include relevant context
_logger.LogError(exception, "Failed to process payment for order {OrderId}", orderId);

// WRONG - Missing exception parameter
_logger.LogError($"Failed to process payment: {exception.Message}");

Correlation IDs

public sealed class CorrelationIdMiddleware : IMiddleware
{
    private const string CorrelationIdHeader = "X-Correlation-Id";

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        var correlationId = context.Request.Headers[CorrelationIdHeader].FirstOrDefault()
            ?? Guid.NewGuid().ToString();

        context.Response.Headers[CorrelationIdHeader] = correlationId;

        using (LogContext.PushProperty("CorrelationId", correlationId))
        {
            await next(context);
        }
    }
}