Add Logging to .NET Core 3.1 WebApi

Content

Add Logging to .NET Core 3.1 WebApi

Goal

Activate and use logging of .NET Core. Implement and configure 3rd party logging (Serilog).

Although .NET Core knows about logging (ILogger), it has no built-in file logger.

Before you start, you should get some basic understanding of the configuration mechanics in ASP.NET Core: https://github.com/boeschenstein/aspnetcore3_configuration

What you should bring

Some basic understanding of

Windows
.NET Core and C#
npm, node
Web technology

About Logging

You have to be familiar with "Development" environment settings (appsettings.json vs. appsettings.Development.json)
If you have additional appsettings.json/appsettings.Development.json in subsequent assemblies, they will overwrite the main/entry settings
If you call others than dll (WebApi), new setup and settings (NLog,SeriLog, ILogger) are needed
Im theory, you can mix both: _logger.LogInformation (ILogger) or native functions (_nlog.Info or serilog). But then you should to keep the minimum severity level (appsettings.json vs. nlog.config or serilog config) in sync

Use Logging in ASP.NET Core projects

Get a .NET WebAPI project

Use your own .NET Core 3.1 WebApi backend.

Alternatively you can clone my sample from here: https://github.com/boeschenstein/angular9-dotnetcore3

If you are new to web development: download the code, open cmd in the folder \frontend and enter "npm i" to install the node modules.

.NET Core is prepared for logging

Unlike the old .NET versions, .NET Core is prepared for logging. It comes with some interfaces like ILogger<T>. Here an example from \WebApplication1\WebApplication1\Controllers\WeatherForecastController.cs, where the logger gets injected in the constructor:

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

Write some Log in your application...

[HttpGet]
public IEnumerable<WeatherForecast> Get()
{
    // https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.logging.loglevel?view=dotnet-plat-ext-5.0
    _logger.LogTrace("Get() was called! (trace)"); // lowest prio, highest verbosity
    _logger.LogDebug("Get() was called! (debug)");
    _logger.LogInformation("Get() was called! (information)");
    _logger.LogWarning("Get() was called! (warning)");
    _logger.LogError("Get() was called! (error)");
    _logger.LogCritical("Get() was called! (critical)"); // highest prio
    ...
}

... run your application, read data from backend (open https://localhost:5001/weatherforecast to call the Get() function of the controller) and check the Output window in Visual Studio (Menu: Debug: Windows: Output):

...
MyBackend.Controllers.WeatherForecastController: Information: Get() was called! (information)
MyBackend.Controllers.WeatherForecastController: Warning: Get() was called! (warning)
...
MyBackend.Controllers.WeatherForecastController: Error: Get() was called! (error)
MyBackend.Controllers.WeatherForecastController: Critical: Get() was called! (critical)
...

Global Error Handling (Middleware)

public class ErrorHandling
{
    private readonly RequestDelegate _next;
    private readonly ILogger _logger;

    public ErrorHandling(RequestDelegate next, ILogger<ErrorHandling> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        try
        {
            // log for development purpose
            _logger.LogInformation($"Request: To:{httpContext.Request.Path} Method:{httpContext.Request.Method}");
            await _next(httpContext);
        }
        // wrong methods called within the core, not to blame to the client
        catch (InvalidOperationException ex)
        {
            _logger.LogError(ex, $"Invalid Operation! {ex.Message}");

            httpContext.Response.Clear();
            httpContext.Response.StatusCode = StatusCodes.Status400BadRequest;
            httpContext.Response.ContentType = "application/json";
            await httpContext.Response.WriteAsync(JsonConvert.SerializeObject(ex.Message));
        }
        catch (ArgumentException ex)
        {
            _logger.LogError(ex, $"Invalid Argument! {ex.Message}");

            httpContext.Response.Clear();
            httpContext.Response.StatusCode = StatusCodes.Status400BadRequest;
            httpContext.Response.ContentType = "application/json";
            await httpContext.Response.WriteAsync(JsonConvert.SerializeObject(ex.Message));
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, $"Exception! {ex.Message}");

            if (httpContext.Response.HasStarted)
            {
                _logger.LogWarning("The response has already started, the http status code middleware will not be executed.");
                throw;
            }

            httpContext.Response.Clear();
            httpContext.Response.StatusCode = StatusCodes.Status500InternalServerError;
            httpContext.Response.ContentType = "application/json";
            await httpContext.Response.WriteAsync(JsonConvert.SerializeObject(ex.Message));
        }
    }
}

// Extension method used to add the middleware to the HTTP request pipeline.
public static class ExceptionHandlingExtensions
{
    public static IApplicationBuilder UseCustomExceptionHandling(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<ErrorHandling>();
    }
}

Serilog

Example 1: Serilog: Basic Implementation without settings in appsettings.json

Install Serilog (Example 1)

Open cmd in the folder with the project file (.csproj) file.

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

Config and implement Serilog (Example 1)

Add a basic Logger (Serilog) configuration:

using Serilog;

public static int Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .WriteTo.Console()
        .WriteTo.File("logs\\log.txt", rollingInterval: RollingInterval.Day) // default log file name pattern: \logs\log{yyymmdd}.txt
        .Enrich.FromLogContext()
        .CreateLogger();

    CreateHostBuilder(args).Build().Run();
}

To log any startup errors, add a try-catch in `Main.cs`:

using Serilog;
using Serilog.Events;

public static int Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .WriteTo.Console()
        .WriteTo.File("logs\\log.txt", rollingInterval: RollingInterval.Day) // default log file name pattern: \logs\log{yyymmdd}.txt
        .Enrich.FromLogContext()
        .CreateLogger();
    try
    {
        Log.Information("Starting web host");
        CreateHostBuilder(args).Build().Run(); // Serilog: this line was already there. The other lines have been added
        return 0;
    }
    catch (Exception ex)
    {
        Log.Fatal(ex, "Host terminated unexpectedly");
        return 1;
    }
    finally
    {
        Log.CloseAndFlush();
    }
}

Activate Serilog (Example 1)

Add the last line in CreateHostBuilder() in Main.cs:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host
    // ...
    .UseSerilog(); // Serilog: add this line

When you start the application, you see the log file in this folder: \<your_webapi_project>\logs\log20200420.txt

Pros/Cons of this approach (Example 1)

Pro: Early initialization: Application startup log is included.
Con: The logger is not configured in appsettings.json.

Example 2: Serilog: Basic Implementation with appsettings.json

InlineInitializationSample

Install Serilog (Example 2)

Open cmd in the folder with the project file (.csproj) file and add the following libraries:

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

Load Configuration from appsettings.config (Example 2)

In program.cs, add this to the CreateDefaultBuilder call:

    .UseSerilog((hostingContext, loggerConfiguration) => loggerConfiguration
        .ReadFrom.Configuration(hostingContext.Configuration)
        .Enrich.FromLogContext()
        .WriteTo.Debug()
        .WriteTo.Console()
      //.WriteTo.Console(outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}") // enhanced logging example
        ;

Here you can find the complete code of `program.cs`:

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using Serilog;

namespace MyBackend
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                })
              .UseSerilog((hostingContext, loggerConfiguration) => loggerConfiguration
                .ReadFrom.Configuration(hostingContext.Configuration)
                .Enrich.FromLogContext()
                .WriteTo.Debug()
                .WriteTo.Console()
              //.WriteTo.Console(outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}") // enhanced logging example
            );
    }
}

Serilog config in appsettings.json (Example 2)

Serilog does not need this "Logging" section, you can delete this:

  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },

This is the complete appsettings.json for Serilog with rolling file:

{
  "Serilog": {
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "logs\\myApplication.log",
          "rollingInterval": "Day"
        }
      }
    ]
  },
  "AllowedHosts": "*"
}

Run the application and you will see the log file here \<your_webapi_project>\logs\myApplication20200420.txt

Pros/Cons of this approach (Example 2)

Con: no Early initialization: Application startup log is not included.
Pro: The logger is configured in appsettings.json.

Example 3: Early Initialization and config in appsettings.json

Install Serilog (Example 3)

Open cmd in the folder with the project file (.csproj) file and add the following libraries:

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

Early initialization and Load Configuration from appsettings.config

public class Program
{
    // source: https://github.com/serilog/serilog-aspnetcore/blob/dev/samples/EarlyInitializationSample/Program.cs

    public static IConfiguration Configuration { get; } = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
        .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
        .AddEnvironmentVariables()
        .Build();

        public static int Main(string[] args)
        {
            Log.Logger = new LoggerConfiguration()
                .ReadFrom.Configuration(Configuration)
                .Enrich.FromLogContext()
                .WriteTo.Debug()
                .WriteTo.Console()
                // .WriteTo.Console(outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}") // enhanced logging example
                .CreateLogger();

           CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                ...
                .UseSerilog() // <-- add this line
                ;
}

Here is the complete source. It adds try-cast around the run() function;

Serilog config in appsettings.json (Example 3)

Serilog does not need this "Logging" section, this is the complete appsettings.json for Serilog with rolling file:

{
  "Serilog": {
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "logs\\myApplication.log",
          "rollingInterval": "Day"
        }
      }
    ]
  },
  "AllowedHosts": "*"
}

Run the application and you will see the log file here \<your_webapi_project>\logs\myApplication20200420.txt

Pros/Cons of this approach (Example 3)

Con: not very obvious/consistent.
Con: manually rebuild initialization order and logic of CreateDefaultBuilder
Pro: The logger is configured in appsettings.json.
Pro: Early initialization: Application startup log is included.

Request Logging

To add request logging, call UseSerilogRequestLogging():

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseSerilogRequestLogging(); // <-- Add this line

    // ... add other app configuration below this ...

Structured logging

https://github.com/serilog/serilog/wiki/Structured-Data

Fixes this issue: https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca2254

Serilog Packages

Package	Function	Status	GitHub
Serilog.AspNetCore	Core functionality
Serilog.Enrichers.Environment
Serilog.Settings.Configuration	reads appsettings.json		https://github.com/serilog/serilog-settings-configuration
Serilog.Sinks.Async
Serilog.Sinks.Console
Serilog.Sinks.RollingFile	Rolling file logging	Deprecated: use Serilog.Sinks.File	https://github.com/serilog/serilog-sinks-rollingfile
Serilog.Sinks.File	normal file logging (not rolling)		https://github.com/serilog/serilog-sinks-file
Serilog.Sinks.Seq
Microsoft.Extensions.Configuration
Microsoft.Extensions.Configuration.Json

NLog

Source: https://github.com/NLog/NLog/wiki/Getting-started-with-.NET-Core-2---Console-application

Add nlog.config file to the entry project:

<?xml version="1.0" encoding="utf-8" ?>
<!-- XSD manual extracted from package NLog.Schema: https://www.nuget.org/packages/NLog.Schema-->
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xsi:schemaLocation="NLog NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      internalLogFile="c:\temp\console-example-internal.log"
      internalLogLevel="Info" >
  <targets>
    <target xsi:type="File" name="target1" fileName="console-example-${shortdate}.log"
            layout="${longdate}|${event-properties:item=EventId_Id}|${level:uppercase=true}|${message} ${exception}|${logger}|${all-event-properties}" />
    <target xsi:type="Console" name="target2"
            layout="${date}|${level:uppercase=true}|${message} ${exception}|${logger}|${all-event-properties}" />
  </targets>
  <rules>
    <logger name="*" minlevel="Trace" writeTo="target1,target2" />
  </rules>
</nlog>

Use the logger:

// Constructor Dependency Injection
public Tester(ILogger<Tester> logger)
{
    // .NET Core ILogger<T>
    logger.LogInformation("Hello from Tester - .NET Core ILogger<T>");

    // Native NLog logger (no DI needed - nice for simpler unit testing)
    Logger log = LogManager.GetCurrentClassLogger();
    log.Info("Hello from Tester - NLog native");
}

Implement NLog in Console

Add NLog

install-package NLog

Load nlog config file:

serviceCollection.AddLogging(builder =>
{
    builder.SetMinimumLevel(LogLevel.Information); // this is the Default if you set "Default" in appsettings.json
    builder.AddNLog("nlog.config");
});

Implement NLog in ASP.NET Core 3

Add NLog

install-package NLog.Web.AspNetCore
install-package NLog

Use this program class

public class Program
{
    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 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 IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                })
            .ConfigureLogging(logging =>
                {
                    logging.ClearProviders();
                    logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace); // this is the Default if you set "Default" in appsettings.json
                })
            .UseNLog();  // NLog: Setup NLog for Dependency injection;
}

Log a static class (ILoggerFactory available)

public static void CancelRunningJobsBeforeHangfireServerStarts(JobStorage currentJobStorage, ILoggerFactory loggerFactory)
{
    var logger = loggerFactory.CreateLogger($"{nameof(ApplicationConfiguration)}"); // use non-generic logger creator
}

Log from class without constructor injection (IServiceCollection available)

public NoMissedRunsAttribute(IServiceCollection services)
{
    _services = services;
}

public void OnCreating(CreatingContext filterContext)
{
    using (var loggerFactory = _services.BuildServiceProvider().GetService<ILoggerFactory>())
    {
        var logger = loggerFactory.CreateLogger<NoMissedRunsAttribute>();

        logger.LogDebug($"Hangfire Filter OnCreating!");
    }
}

What's next

Swagger/OpenApi are tools which can create your Angular code to access the backend: check this https://github.com/boeschenstein/angular9-dotnetcore-openapi-swagger

Additional Information

Links

.NET Core configuration: https://github.com/boeschenstein/aspnetcore3_configuration
.NET Core logging: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-3.1
Third-party logging providers: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-3.1#third-party-logging-providers
Serilog
- https://github.com/serilog/serilog-aspnetcore
- Setting up Serilog in ASP.NET Core 3: https://nblumhardt.com/2019/10/serilog-in-aspnetcore-3/
NLog
- .NET Core Console: https://github.com/NLog/NLog/wiki/Getting-started-with-.NET-Core-2---Console-application
- ASP.NET Core 3: https://github.com/NLog/NLog/wiki/Getting-started-with-ASP.NET-Core-3
Log levels: https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.logging.loglevel
Generic Host builder (Core 3) replaces Web Host Builder (Core 2): https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/web-host?view=aspnetcore-3.1
ASP.NET WebApi: https://docs.microsoft.com/en-us/aspnet/core/tutorials/first-web-api?view=aspnetcore-3.1&tabs=visual-studio
About me: https://github.com/boeschenstein

Current Versions

Visual Studio 2019 16.5.4
.NET core 3.1
npm 6.14.4
node 12.16.1
Angular CLI 9.1
Serilog.AspNetCore 3.2.0
Serilog.Sinks.File 4.1.0

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