Scott Hanselman

You've long been able to write Windows Services in .NET and .NET Core, and you could certainly write a vanilla Console App and cobble something together for a long running headless service as well. However, the idea of a Worker Process, especially a long running one is a core part of any operating system - Windows, Linux, or Mac.

Now that open source .NET Core is cross-platform, it's more than reasonable to want to write OS services in .NET Core. You might write a Windows Service with .NET Core or a systemd process for Linux with it as well.

Go grab a copy of .NET Core 3.0 - as of the time of this writing it's very close to release, and Preview 8 is supported in Production.

If you're making a Windows Service, you can use the Microsoft.Extensions.Hosting.WindowsService package and tell your new Worker that its lifetime is based on ServiceBase.

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseWindowsService()
        .ConfigureServices(services =>
        {
            services.AddHostedService<Worker>();
        });

If you're making a Linux worker and using systemd you'd add the Microsoft.Extensions.Hosting.Systemd package and tell your new Worker that its lifetime is managed by systemd!

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseSystemd()
        .ConfigureServices((hostContext, services) =>
        {
            services.AddHostedService<Worker>();
        });

The Worker template in .NET Core makes all this super easy and familiar if you're used to using .NET already. For example, logging is built in and regular .NET log levels like LogLevel.Debug or LogLevel.Critical are automatically mapped to systemd levels like Debug and Crit so I could run something like sudo journalctl -p 3 -u testapp and see my app's logs, just alike any other Linux process because it is!

You'll notice that a Worker doesn't look like a Console App. It has a Main but your work is done in a Worker class. A hosted service or services is added with AddHostedService and then a lot of work is abstracted away from you. The Worker template and BackgroundService base class brings a lot of the useful conveniences you're used to from ASP.NET over to your Worker Service. You get dependency injection, logging, process lifetime management as seen above, etc, for free!

public class Worker : BackgroundService
{
    private readonly ILogger<Worker> _logger;

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

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
            await Task.Delay(1000, stoppingToken);
        }
    }
}

This is a very useful template and it's available from the command line as "dotnet new worker" or from File New Project in Visual Studio 2019 Preview channel.

Also check out Brady Gaster's excellent blog post on running .NET Core workers in containers in Azure Container Instances (ACI). This is super useful if you have some .NET Core and you want to Do A Thing in the cloud but you also want per-second billing for your container.

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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