How To Implement Logging in ASP.NET Core.

Logging is the process of recording application events so you can:

• Debug issues
• Monitor behavior
• Trace requests
• Audit actions in production

Without proper logging:

• Bugs are hard to reproduce
• Production failures are invisible
• Root cause analysis becomes guesswork

ASP.NET Core has ILogger built in via Microsoft.Extensions.Logging. Supported Providers (by default)

• Console
• Debug
• EventSource
• Application Insights (Azure)

Rule: Never log everything as Information.

How To Use ILogger?

Step 1: Inject ILogger.

public class OrderController : ControllerBase
{
    private readonly ILogger<OrderController> _logger;

    public OrderController(ILogger<OrderController> logger)
    {
        _logger = logger;
    }
}

Step 2: Log Messages

_logger.LogInformation("Order creation started");

_logger.LogWarning("Order {OrderId} has no items", orderId);

_logger.LogError(exception, "Failed to create order {OrderId}", orderId);

Good Option 1: Logging Exception Correctly.

catch (Exception ex)
{
    _logger.LogError(ex, "Error while processing order {OrderId}", orderId);
    throw;
}

👉 Always pass the exception object to preserve stthe ack trace.

Good Option 2: Logging in Middleware.

public async Task InvokeAsync(HttpContext context)
{
    _logger.LogInformation(
        "Request {Method} {Path}",
        context.Request.Method,
        context.Request.Path);

    await _next(context);

    _logger.LogInformation(
        "Response {StatusCode}",
        context.Response.StatusCode);
}

Built-in logging is good, but Serilog is preferred in production because it provides:

• Rich structured logging
• Multiple sinks (File, DB, Seq, Elastic)
• Better performance & flexibility

Step 1: Install Packages

dotnet add package Serilog.AspNetCore
dotnet add package Serilog.Sinks.Console
dotnet add package Serilog.Sinks.File

Step 2: Configure Serilog in Program.cs

using Serilog;

Log.Logger = new LoggerConfiguration()
    .Enrich.FromLogContext()
    .WriteTo.Console()
    .WriteTo.File("Logs/app-.log", rollingInterval: RollingInterval.Day)
    .CreateLogger();

builder.Host.UseSerilog();

Step 3: Use ILogger as Usual.

_logger.LogInformation("Invoice {InvoiceId} generated", invoiceId);

You still use ILoggerSerilog works behind the scenes.

Interview Answer: In ASP.NET Core, I use ILogger for application logging and Serilog for structured, production-grade logging. I follow proper log levels, structured messages, correlation IDs, and centralized log storage to ensure observability and easy debugging.