Dotnet Worker Services

.NET Worker Services

Overview

.NET Worker Services are long-running background applications built on the Generic Host (Microsoft.Extensions.Hosting). They use BackgroundService or IHostedService to run tasks that operate independently of HTTP requests, such as queue processing, scheduled jobs, file watching, and health monitoring.

Worker services support the same DI, configuration, logging, and lifetime management as ASP.NET Core applications. They can run as console applications, Windows services (via Microsoft.Extensions.Hosting.WindowsServices), or Linux systemd daemons (via Microsoft.Extensions.Hosting.Systemd).

Create a new worker service:

dotnet new worker -n MyWorker

Install platform-specific hosting packages:

dotnet add package Microsoft.Extensions.Hosting.WindowsServices
dotnet add package Microsoft.Extensions.Hosting.Systemd

Basic BackgroundService

BackgroundService is the standard base class for implementing long-running tasks. Override ExecuteAsync with your processing loop.

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

public class QueueProcessingWorker : BackgroundService
{
    private readonly ILogger<QueueProcessingWorker> _logger;
    private readonly IMessageQueue _queue;

    public QueueProcessingWorker(
        ILogger<QueueProcessingWorker> logger,
        IMessageQueue queue)
    {
        _logger = logger;
        _queue = queue;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Queue processor starting");

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                var message = await _queue.DequeueAsync(stoppingToken);
                if (message is not null)
                {
                    await ProcessMessageAsync(message, stoppingToken);
                }
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                // Graceful shutdown requested
                break;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error processing message");
                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken);
            }
        }

        _logger.LogInformation("Queue processor stopped");
    }

    private async Task ProcessMessageAsync(Message message, CancellationToken token)
    {
        _logger.LogInformation("Processing message {Id}", message.Id);
        // Processing logic here
        await Task.CompletedTask;
    }
}

Host Configuration and Registration

Configure the host with DI, logging, configuration, and one or more hosted services.

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

var builder = Host.CreateApplicationBuilder(args);

// Configure services
builder.Services.AddSingleton<IMessageQueue, InMemoryMessageQueue>();
builder.Services.AddHostedService<QueueProcessingWorker>();
builder.Services.AddHostedService<HealthCheckWorker>();

// Configure for Windows service or systemd
builder.Services.AddWindowsService(options =>
{
    options.ServiceName = "MyWorkerService";
});
builder.Services.AddSystemd();

// Configure logging
builder.Logging.AddConsole();
builder.Logging.AddEventLog(); // Windows only

using var host = builder.Build();
await host.RunAsync();

Scoped Services in Workers

BackgroundService is registered as a singleton, so you cannot inject scoped services directly. Create a scope manually for each unit of work.

using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

public class ScopedProcessingWorker : BackgroundService
{
    private readonly IServiceScopeFactory _scopeFactory;
    private readonly ILogger<ScopedProcessingWorker> _logger;

    public ScopedProcessingWorker(
        IServiceScopeFactory scopeFactory,
        ILogger<ScopedProcessingWorker> logger)
    {
        _scopeFactory = scopeFactory;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            using (var scope = _scopeFactory.CreateScope())
            {
                var dbContext = scope.ServiceProvider.GetRequiredService<AppDbContext>();
                var processor = scope.ServiceProvider.GetRequiredService<IOrderProcessor>();

                var pendingOrders = await dbContext.Orders
                    .Where(o => o.Status == OrderStatus.Pending)
                    .ToListAsync(stoppingToken);

                foreach (var order in pendingOrders)
                {
                    await processor.ProcessAsync(order, stoppingToken);
                }
            }

            await Task.Delay(TimeSpan.FromMinutes(1), stoppingToken);
        }
    }
}

Timed Background Tasks with PeriodicTimer

Use PeriodicTimer (introduced in .NET 6) for precise interval scheduling that does not drift over time.

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

public class HealthCheckWorker : BackgroundService
{
    private readonly ILogger<HealthCheckWorker> _logger;
    private readonly TimeProvider _timeProvider;

    public HealthCheckWorker(
        ILogger<HealthCheckWorker> logger,
        TimeProvider timeProvider)
    {
        _logger = logger;
        _timeProvider = timeProvider;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using var timer = new PeriodicTimer(TimeSpan.FromSeconds(30));

        while (await timer.WaitForNextTickAsync(stoppingToken))
        {
            var timestamp = _timeProvider.GetUtcNow();
            _logger.LogDebug("Health check at {Timestamp}", timestamp);

            try
            {
                await CheckDependenciesAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Health check failed");
            }
        }
    }

    private async Task CheckDependenciesAsync(CancellationToken token)
    {
        // Check database, external APIs, etc.
        await Task.CompletedTask;
    }
}

IHostedService vs BackgroundService

Graceful Shutdown with IHostApplicationLifetime

Hook into application lifecycle events for cleanup, flushing buffers, or draining in-flight work.

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

public class GracefulWorker : IHostedService
{
    private readonly ILogger<GracefulWorker> _logger;
    private readonly IHostApplicationLifetime _lifetime;
    private Task? _executingTask;
    private CancellationTokenSource? _cts;

    public GracefulWorker(
        ILogger<GracefulWorker> logger,
        IHostApplicationLifetime lifetime)
    {
        _logger = logger;
        _lifetime = lifetime;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);

        _lifetime.ApplicationStopping.Register(() =>
        {
            _logger.LogInformation("Shutdown signal received, draining work...");
        });

        _executingTask = RunAsync(_cts.Token);
        return Task.CompletedTask;
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        if (_executingTask is null) return;

        _cts?.Cancel();

        await Task.WhenAny(_executingTask, Task.Delay(Timeout.Infinite, cancellationToken));
        _logger.LogInformation("Worker stopped gracefully");
    }

    private async Task RunAsync(CancellationToken token)
    {
        while (!token.IsCancellationRequested)
        {
            await Task.Delay(TimeSpan.FromSeconds(10), token);
        }
    }
}

Configuring Shutdown Timeout

By default, the host waits 30 seconds for hosted services to stop. Configure this in appsettings.json or via host options.

using Microsoft.Extensions.Hosting;

var builder = Host.CreateApplicationBuilder(args);

builder.Services.Configure<HostOptions>(options =>
{
    options.ShutdownTimeout = TimeSpan.FromSeconds(60);
    options.BackgroundServiceExceptionBehavior = BackgroundServiceExceptionBehavior.Ignore;
});

Best Practices

1. Always respect the stoppingToken passed to ExecuteAsync -- check IsCancellationRequested in loops and pass the token to all async calls including Task.Delay.
2. Use IServiceScopeFactory to create scoped services inside worker loops because BackgroundService is a singleton and cannot inject scoped dependencies directly.
3. Catch OperationCanceledException separately from other exceptions in your main loop to distinguish graceful shutdown from actual errors.
4. Use PeriodicTimer instead of Task.Delay in a loop for timed tasks because PeriodicTimer accounts for processing time and does not drift.
5. Configure BackgroundServiceExceptionBehavior explicitly -- the default in .NET 8+ stops the host on unhandled exceptions, which may not be desired for resilient workers.
6. Set the shutdown timeout via HostOptions.ShutdownTimeout to give workers enough time to finish in-flight work before the process is killed.
7. Log at startup and shutdown boundaries in every worker to make it easy to diagnose when and why a service started or stopped.
8. Avoid blocking StartAsync when implementing IHostedService directly -- start your background task and return immediately so other hosted services can start.
9. Use AddWindowsService() or AddSystemd() for production deployments so the worker integrates properly with the OS service manager for lifecycle events.
10. Register multiple BackgroundService implementations for independent concerns (queue processing, health checks, cleanup) rather than combining them into a single monolithic worker.