IHostedService .NET 6 not starting when deployed - .net-6.0

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

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)

Answer 2

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