Method 1: Explicit Repository Configuration

Required NuGet packages: log4net and Microsoft.Extensions.Logging.Log4Net.AspNetCore

Initialize reposiotry during application startup:

public Startup(IConfiguration config, IWebHostEnvironment env)
{
    string appRoot = env.ContentRootPath;
    FileInfo configFile = new FileInfo(Path.Combine(appRoot, "Config", "log4net.xml"));
    
    ILoggerRepository repo = LogManager.CreateRepository("PrimaryRepo");
    XmlConfigurator.Configure(repo, configFile);
}

Usage example:

ILog logger = LogManager.GetLogger("PrimaryRepo", typeof(Startup));
logger.Info("Informational message");
logger.Warn("Warning notification");

Method 2: Default Repository via Builder

Configure through host builder:

public static IHostBuilder CreateHost(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder => 
        {
            webBuilder.UseStartup<Startup>();
        })
        .ConfigureLogging(logConfig =>
        {
            logConfig.AddFilter("System", LogLevel.Warning);
            logConfig.AddFilter("Microsoft", LogLevel.Warning);
            logConfig.AddLog4Net("Config/log4net.xml");
        });

Basic usage:

ILog log = LogManager.GetLogger(typeof(Program));
log.Debug("Debug trace");
log.Error("Exception occurred");

Alternative using factory:

ILoggerFactory loggerFactory = ... // Injected dependency
loggerFactory.CreateLogger<T>().LogError("Error message");
loggerFactory.CreateLogger<T>().LogWarning("Warning notice");

Controller implementation:

using Microsoft.Extensions.Logging;

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;

    public HomeController(ILogger<HomeController> logger)
    {
        _logger = logger;
    }
    
    public IActionResult Index()
    {
        _logger.LogError("Controller error");
        return View();
    }
}