c# - Use NLog in ASP.NET Core application

Question

I found a CodeProject with an example of how to get this to work, but it doesn't work. The main problem seems to be that the "Microsoft.Framework.Logging.NLog": "1.0.0-*" package doesn't seem to exist in Nuget. I've looked at this StackOverflow question and looked at the GitHub example it references, but it seems to contain the same issue.

I've tried to get it working on my own and the best I've come up with is the following:

public class NLogLogger : ILogger
{
    public NLogLogger()
    {
        new WebLoggerConfigurer().ConfigureDefault();
    }

    public void Log(LogLevel logLevel, int eventId, object state, Exception exception, Func<object, Exception, string> formatter)
    {
        // currently need the global:: for LogLevels because our namespace contains NLog in it. Is there a better naming convention we could use instead?
        var ll = logLevel == LogLevel.Debug ? global::NLog.LogLevel.Debug
                : logLevel == LogLevel.Verbose ? global::NLog.LogLevel.Trace
                : logLevel == LogLevel.Critical ? global::NLog.LogLevel.Fatal
                : logLevel == LogLevel.Error ? global::NLog.LogLevel.Error
                : logLevel == LogLevel.Information ? global::NLog.LogLevel.Info
                : logLevel == LogLevel.Warning ? global::NLog.LogLevel.Warn
                : global::NLog.LogLevel.Off;

        LogManager.GetCurrentClassLogger().Log(ll, formatter(state, exception));
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        return true;
    }

    public IDisposable BeginScopeImpl(object state)
    {
        return new Disposable(() => { });
    }
}

public class NLogLoggerProvider : ILoggerProvider
{
    public void Dispose()
    {
    }

    public ILogger CreateLogger(string categoryName)
    {
        return new NLogLogger();
    }
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.AddProvider(new NLogLoggerProvider());
    ..
}

The implementation of BeginScopeImpl seems to be a hack, but I was unsure how best to implement it.

1. Does this seem like a valid implementation option?
2. Is there some better way of implementing BeginScopeImpl?
3. Is there another way of getting NLog to work with ASP.NET Core?

Answer 1

Microsoft.Framework.Logging.NLog has been replaced by NLog.Extensions.Logging on NuGet, which is maintained by the NLog team.

For ASP.NET Core, you need NLog.Web.AspNetCore (which has a dependency on NLog.Extensions.Logging).

How to use:

Setup

NLog needs to be enabled so it will integrate into the DI and log API of ASP.NET Core. This will result that all logs written by externals (e.g. Microsoft) will be also sent to NLog - you could filter that out in the NLog's config (without performance impact).

Since ASP.NET Core 2 there are new approach.

ASP.NET Core 1

In ASP.NET Core in Configure and optionally ConfigureServices needs to be updated.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    //add NLog to .NET Core
    loggerFactory.AddNLog();

    //Enable ASP.NET Core features (NLog.web) - only needed for ASP.NET Core users
    app.AddNLogWeb();

    //configure nlog.config in your project root. 
    env.ConfigureNLog("nlog.config");
    ...
    //you could use LogManager.Configuration from here


public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    // e.g. services.AddMvc();

    //needed for NLog.Web
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
}

ASP.NET Core 2

For ASP.NET Core 2, the setup is different than in ASP.NET Core 1

Set-up NLog in program.cs:

using NLog.Web;
using Microsoft.Extensions.Logging;

public static void Main(string[] args)
{
    // NLog: setup the logger first to catch all errors
    var logger = NLog.Web.NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
    try
    {
        logger.Debug("init main");
        CreateWebHostBuilder(args).Build().Run(); 
    }
    catch (Exception ex)
    {
        //NLog: catch setup errors
        logger.Error(ex, "Stopped program because of exception");
        throw;
    }
    finally
    {
        // Ensure to flush and stop internal timers/threads before application-exit (Avoid segmentation fault on Linux)
        NLog.LogManager.Shutdown();
    }
}

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>()
        .ConfigureLogging(logging =>
        {
            logging.ClearProviders();
            logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
        })
        .UseNLog();  // NLog: setup NLog for Dependency injection

ASP.NET Core 3 & 5

There are some small changes compared to ASP.NET Core 2, e.g. there is an IHostBuilder instead of the IWebHostBuilder.

For ASP.NET Core 5 the steps are the same.

Set-up NLog in program.cs:

using System;
using NLog.Web;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Hosting;

public static void Main(string[] args)
{
    var logger = NLog.Web.NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
    try
    {
        logger.Debug("init main");
        CreateHostBuilder(args).Build().Run();
    }
    catch (Exception exception)
    {
        //NLog: catch setup errors
        logger.Error(exception, "Stopped program because of exception");
        throw;

    }
    finally
    {
        // Ensure to flush and stop internal timers/threads before application-exit (Avoid segmentation fault on Linux)
        NLog.LogManager.Shutdown();
    }
}

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
      .ConfigureWebHostDefaults(webBuilder =>
      {
          webBuilder.UseStartup<Startup>();
      })
      .ConfigureLogging(logging =>
      {
          logging.ClearProviders();
          logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
      })
      .UseNLog();  // NLog: Setup NLog for Dependency injection

Write logs

Inject an ILogger with the class type as generic argument.

public class HomeController : Controller
{
    public HomeController(ILogger<HomeController> logger)
    {
        logger.LogInformation("created homeController");
    }

Configure NLog rules

Example on how to configure, log and filter.

Create an nlog.config (for more reading about nlog.config, see docs).

This example will create 2 files, one with all the logs (including Microsoft's) and a file with only your logs.

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        autoReload="true"
        internalLogLevel="Warn"
        internalLogFile="c:empinternal.txt">


    <extensions>
        <!--enable NLog.Web for ASP.NET Core-->
        <add assembly="NLog.Web.AspNetCore"/>
    </extensions>

    <!-- define various log targets -->
    <targets>
        <!-- write logs to file -->
        <target xsi:type="File" name="allfile" fileName="c:emp
log-all-${shortdate}.log"
                        layout="${longdate}|${logger}|${uppercase:${level}}|${message} ${exception}" />

        <target xsi:type="File" name="ownFile" fileName="c:emp
log-own-${shortdate}.log"
                    layout="${longdate}|${logger}|${uppercase:${level}}|${message} ${exception}" />

    </targets>

    <rules>
        <!--All logs, including from Microsoft-->
        <logger name="*" minlevel="Trace" writeTo="allfile" />

        <!--Skip Microsoft logs - no writeTo attribute-->
        <logger name="Microsoft.*" minlevel="Trace" final="true" />
        <logger name="*" minlevel="Trace" writeTo="ownFile" />
    </rules>
</nlog>

Publish nlog.config

this isn't a required step for ASP.NET Core 5

Make sure that the nlog.config will be published, e.g in your csproj file:

<ItemGroup>
    <Content Update="nlog.config" CopyToOutputDirectory="PreserveNewest" />
</ItemGroup>

Output

"nlog-own-2018-02-14.log" contains:

2018-02-14 16:27:04.0547|aspnetCoreApplication.Controllers|INFO|created homeController

2018-02-14 16:27:04.0547|aspnetCoreApplication.Controllers|INFO|created homeController

Troubleshoot

Missing debug log messages in ASP.NET Core 2? While the we use SetMinimumLevel in program.cs, also appsettings.json could confluence this.

You could change that as follows:

Change appsettings.json:

{
    "Logging": {
        "LogLevel": {
            "Default": "Trace"
        }
    }
}

You could also filter Microsoft's logs here, e.g.

{
    "Logging": {
        "LogLevel": {
            "Default": "Trace",
            "Microsoft": "Information"
        }
    }
}

Other issues, see this step plan to find the cause: Logging-troubleshooting in NLog

Cheers,

Julian (NLog)

Edit: updated for NLog.Web.AspNetCore 4.3

Edit 2: Updated for ASP.NET Core 2 and latest recommendations

Edit 3: Updated for ASP.NET Core 3

Edit 4: updated for ASP.NET Core 5