Dependency injection (with IOptions) in Console Apps in .NET Core

When you are used to building web applications, you kind of get hooked to the ease of Dependency Injection (DI) and the way settings can be specified in a JSON file and accessed through DI (IOptions<T>). It's only logical to want the same feature in your Console app.

After reading many - many! - outdated blogs, I decided to add my 50 cents specifically on a Console app. It all comes down to packages and separation of concern.

Note: it feels like a bit of over-engineering, but you'll get some nice features in return; the program becomes more pluggable and more testable. It also provides a nice async main function.

Nuget me!

First, we need the right packages. And that can be quite a hassle - because the ASP.NET Core All package will include them for you when you are building an ASP.NET application - but there's no such thing for a Console app. They might be hard to google find:

  • Microsoft.Extensions.Configuration
  • Microsoft.Extensions.Configuration.EnvironmentVariables
  • Microsoft.Extensions.Configuration.FileExtensions
  • Microsoft.Extensions.Configuration.Json
  • Microsoft.Extensions.DependencyInjection
  • Microsoft.Extensions.DependencyInjection.Abstractions
  • Microsoft.Extensions.Logging
  • Microsoft.Extensions.Logging.Console
  • Microsoft.Extensions.Logging.Debug
  • Microsoft.Extensions.Options

The project file

Edit your console project file and replace its contents with this.

<Project Sdk="Microsoft.NET.Sdk">
    <PackageReference Include="Microsoft.Extensions.Configuration" />
    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
    <PackageReference Include="Microsoft.Extensions.Configuration.Json" />
    <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
    <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
    <PackageReference Include="Microsoft.Extensions.Logging" />
    <PackageReference Include="Microsoft.Extensions.Logging.Console" />
    <PackageReference Include="Microsoft.Extensions.Logging.Debug" />
    <PackageReference Include="Microsoft.Extensions.Options" />

Now you can upgrade the packages to the latest version in your Nuget manager (I've omitted versions, as they become outdated and you want the latest). The <LangVersion>latest</LangVersion> will enable the latest version of C# including the async main (needed for .NET Core < 3).

AppSettings class + json

This blog has been around for a while now and people asked for an example of the actual settings. I use this class as AppSettings:

public class AppSettings
    public string TempDirectory { get; set; }

Next, you can add a appsettings.json to the root of your application:

    "App": {
        "TempDirectory": "c:\\temp\\rss-hero\\tmp\\"

Make sure the file has properties: Build Action must be None and Copy to Output Directory must be Copy always. It should like this in your project file:

  <None Update="appsettings.json">

The JSON file works with sections, and we'll see later in the article how we bind the App section to an AppSettings instance. Want to know more about the setup with json files? Please read Setup multiple setting-files with a .NET Console Application.

Program vs. App

Normally the program class contains the main method and all the program-logic. If you want to do DI, it might be handy to separate the application from the setup that's required for your DI. So I propose to build an App class that does the actual running. For argument's sake, I've created such a class with a logger and some settings:

using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System;
using System.Threading.Tasks;

public class App
    private readonly ILogger<App> _logger;
    private readonly AppSettings _appSettings;

    public App(IOptions<AppSettings> appSettings, ILogger<App> logger)
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _appSettings = appSettings?.Value ?? throw new ArgumentNullException(nameof(appSettings));

    public async Task Run(string[] args)

        Console.WriteLine("Hello world!");


        await Task.CompletedTask;

This basically gives us an abstracted application class that is even testable. It also gives us the opportunity to focus on setting up the application in the program class (separating the actual application logic).

Setting up the program

In the program, we'll focus on DI. The App will also be added through DI. Not that the entry point of the program is already async so we can use await.

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System.IO;
using System.Threading.Tasks;

internal class Program
    public static async Task Main(string[] args)
        // create service collection
        var services = new ServiceCollection();

        // create service provider
        var serviceProvider = services.BuildServiceProvider();

        // entry to run app
        await serviceProvider.GetService<App>().Run(args);

    private static void ConfigureServices(IServiceCollection services)
        // configure logging
        services.AddLogging(builder =>

        // build config
        var configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", optional: false)


        // add services:
        // services.AddTransient<IMyRespository, MyConcreteRepository>();

        // add app

We've injected a few things:

  • Logging − a lot of my application run as stand-alone services in Docker containers, so logging is key. For convenience, I added a console logger. You can add any form of logging to the LoggerFactory.
  • Configuration − I use a appsettings.json file in my application. It will contain a section with the app variables. The DI will auto-map it to the setting object. To make things easier I added the AddEnvironmentVariables() so I'm able to override settings in production.
  • Services − this will give us nice abstractions.

The Main method will resolve the App through DI and start your program. So that's it. Easy to use.


2020-04-07: Added .NET 3.1 and support for args in the App.
2019-09-25: Added "Hello World" message and .NET Core 3.0 support.
2019-01-10: Added AppSettings class and JSON config examples.
2018-12-14: Added 2 packages missing in the list of Nuget packages.
2018-12-14: Logging is now done using the logging builder - the other version is obsolete.
2018-12-14: Added async main support by specifying the project example.