IHostedService StopAsync and OnStopping/OnStopped events not called with IIS preload enabled

[lpn-ch]

In summary, if I

• Install the "Application Initialization module" in IIS
• Set "StartMode: AlwaysRunning" for the app pool
• Set "Preload Enabled: True" for the website

The IHostedService StopAsync method and OnStopping/OnStopped events are not called when either recycling the app pool or restarting IIS (iisreset). Just disabling "Preload Enabled" fixes the issue.

Not sure this is an IIS or .Net Core issue.

Here is the output of dotnet --info

Host (useful for support):
Version: 3.1.9
Commit: 774fc3d6a9

.NET Core SDKs installed:
No SDKs were found.

.NET Core runtimes installed:
Microsoft.AspNetCore.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

IIS on Windows Server 2019 1809, but same issue on Windows 10 1909.

Code sample:

public class Program
{
public static void Main(string[] args)
{
CreateHostBuilder(args).Build().Run();
}

public static IHostBuilder CreateHostBuilder(string[] args) =>
	Host.CreateDefaultBuilder(args)
		.ConfigureWebHostDefaults(webBuilder =>
		{
			webBuilder.UseStartup<Startup>();
		})
		.ConfigureServices(services =>
		{
			services.AddHostedService<LifetimeEventsHostedService>();
		});

}

internal class LifetimeEventsHostedService : IHostedService
{
private readonly ILogger _logger;
private readonly IHostApplicationLifetime _appLifetime;

public LifetimeEventsHostedService(
    ILogger<LifetimeEventsHostedService> logger, 
    IHostApplicationLifetime appLifetime)
{
    _logger = logger;
    _appLifetime = appLifetime;
}

public Task StartAsync(CancellationToken cancellationToken)
{
    _appLifetime.ApplicationStarted.Register(OnStarted);
    _appLifetime.ApplicationStopping.Register(OnStopping);
    _appLifetime.ApplicationStopped.Register(OnStopped);

    return Task.CompletedTask;
}

public Task StopAsync(CancellationToken cancellationToken)
{
    _logger.LogInformation("StopAsync has been called.");

    return Task.CompletedTask;
}

private void OnStarted()
{
    _logger.LogInformation("OnStarted has been called.");
}

private void OnStopping()
{
    _logger.LogInformation("OnStopping has been called.");
}

private void OnStopped()
{
    _logger.LogInformation("OnStopped has been called.");
}

}

StartAsync and OnStarted are always called. It seems the process is killed by IIS instead of cleanly shutting down when preload is enabled.

[BrennanConroy]

Could you try this with 5.0?

Also, can you verify that this isn't just an issue with the logs not being flushed by debugging the app on close?

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[lpn-ch]

Could you try this with 5.0?

Also, can you verify that this isn't just an issue with the logs not being flushed by debugging the app on close?

Forgive me for the late reply, I was very busy last week.

After doing more tests, I have more details concerning the issue, but I will first answer your questions.

• .Net 5.0 does not solve the issue.
• It is not a log not flushed issue, I replaced with File.AppendAllText() which closes the file after write and the issue is still there. Also, there would be no reason to log in one case and not the other.

But the issue of the preload not calling stop events on recycle/iisreset is actually a side effect of another issue. If the website does not receive any requests, the stop events are never called on recycle/iisreset. If the website does receive one request, the stop events start getting called on every recycle until an iisreset is done which will be the last to call stop events. This is why the issue is not exhibited with preload disabled since a request has to be done to activate the website, which in turn solves the issue.

Here is the sequence to reproduce:

• Configure preload to work on the app pool and website.
• App pool recycling or iisreset will not call stop events.
• Make a single request on the website.
• App pool recycling or iisreset will call stop events.
• App pool recycling will call stop events until iisreset is executed.

Hope this helps.

[jkotalik]

If the website does not receive any requests, the stop events are never called on recycle/iisreset

In the case where preload is disabled, I believe this expected as the start events haven't been called either.

And to confirm, when you have preload enabled, you see the start events occur without sending a request, but on recycle you don't see the stop events called. Only after sending a request to the server, do you see the stop events called.

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