IHostedService .NET 6 not starting when deployed

Question

I have an API which contains a HostedService that is built in VS2022 with .Net 6.

When I run locally the service is called as expected and everything works fine but when deplyed, the service doesn't seem to start.

I have tried many different configurations and even tried using a background service but it all has the same result. Here is my code:

I have an existing app build in VS2019 .Net Core 3.1 that has a HostedService and is working fine. I noticed that when I converted my .Net Core app to .Net 6, the service did not start when I deployed so I decided to just build a little app to try and find what's causing the issue.

Program.cs

using HostedServices.Services;

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseSerilog((context, loggerConfiguration) => loggerConfiguration
        .ReadFrom.Configuration(context.Configuration)
        .Enrich.FromLogContext()
        .Enrich.WithMachineName());

// Add services to the container.

builder.Services.AddControllers();

builder.Services.AddHostedService<MainService>();
var app = builder.Build();

// Configure the HTTP request pipeline.

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

Here is the Hosted Service

namespace HostedServices.Services
{
    public class MainService : IHostedService, IDisposable
    {
        private int executionCount = 0;
        private readonly ILogger<MainService> _logger;
        private Timer _timer;
        private Task _executingTask;
        private readonly CancellationTokenSource _stoppingCts = new CancellationTokenSource();

        public MainService(ILogger<MainService> logger)
        {
            _logger = logger;
        }
        public Task StartAsync(CancellationToken cancellationToken)
        {
   
            _logger.LogInformation($"Test Hosted Service Started {DateTime.Now}.");
            _timer = new Timer(DoWork, null, TimeSpan.Zero,
                    TimeSpan.FromMinutes(1));

            return Task.CompletedTask;

        }

        private void DoWork(object state)
        {
            _executingTask = DoWorkAsync(_stoppingCts.Token);
        }

        private async Task DoWorkAsync(CancellationToken token)
        {
            _logger.LogInformation(
                    "Doing work: {0}", DateTime.Now);

        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("Service is stopping.");

            _timer?.Change(Timeout.Infinite, 0);

            return Task.CompletedTask;
        }

        public void Dispose()
        {
            _timer?.Dispose();
        }


    }
}

Everything runs fine locally but when I deploy it, the service doesn't seem to start, no log files are generated and I can't seem to find any errors reported.

Any ideas?

Answer 1

The problem is that while IHostedService start when the site starts when does IIS start the site? By default, it doesn't until a request is made. If your site goes idle for a while IIS will kill the thread as well.

IIS has a feature you can enable called "Application Initialization". You then need to configure the Application Pool to always start (startMode="AlwaysRunning").

Lastly, you configure the site's application to preload which sends a fake HTTP request to the site on startup (preloadEnabled="true").

The docs for this are here: https://learn.microsoft.com/en-us/iis/get-started/whats-new-in-iis-8/iis-80-application-initialization

Answer 2

We had the same problem and resolved it by following IIS settings:

• Under "Page" Advanced Settings: "Preload Enabled" must be set to "true" (this forces app to run after every app pool recycle and on startup)
• Under "App Pool" Advanced settings: "Start mode" must be set to "AlwaysRunning"
• "Page" in IIS must have http allowed (since preload enabled works only on http and not via https)