BackgroundService StopAsync not called when stopping Web App in Azure using ASP.NET Core 6 Minimal API

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I created the template Minimal API template with VS 2022 ASP.NET 6.0, and added a BackgroundService as a HostedService. I deployed this to Azure and it starts the Background service fine and i can see it in the logs.

However when i stop the web app in Azure, the StopAsync of the BackgroundService is not called. Do i need to hook something up in the Program.cs with the builder.Host? How in the code can i get notified that the web app is shutting down in case i need to do some other graceful shutdown? Program.cs

using MinAPI.Test.Workers;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

builder.Services.AddHostedService<Worker>();

var app = builder.Build();

app.UseSwagger();
app.UseSwaggerUI();

app.UseHttpsRedirection();

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
       new WeatherForecast
       (
           DateTime.Now.AddDays(index),
           Random.Shared.Next(-20, 55),
           summaries[Random.Shared.Next(summaries.Length)]
       ))
        .ToArray();
    return forecast;
})
.WithName("GetWeatherForecast");

app.Run();

internal record WeatherForecast(DateTime Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}

Worker.cs

namespace MinAPI.Test.Workers
{
    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);
            }

            _logger.LogInformation("Worker cancellation token finished ");
        }

        public override Task StartAsync(CancellationToken cancellationToken)
        {
            _logger.LogWarning("Worker STARTING");
            return base.StartAsync(cancellationToken);
        }

        public override Task StopAsync(CancellationToken cancellationToken)
        {
            _logger.LogWarning("Worker STOPPING: {time}", DateTimeOffset.Now);
            return base.StopAsync(cancellationToken);
        }
    }
}

Expected Behavior

I would expect the line _logger.LogWarning(“Worker STOPPING: {time}”, DateTimeOffset.Now); to be hit when stopping in Azure.

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

.Net 6

Anything else?

No response

[jez9999]

This is a known issue for which there is a similar existing issue specific to the Worker template prior to 6.0. App Service essentially sends a different shutdown command. There is no plan to resolve this in the app service side, nor known workaround when one is running their Worker in app service. Have you tried running your worker in Azure Container Apps or in Azure Container Instances? Those options don’t have this same issue.

Out of interest why is it such a difficult fix for App Service just to send a SIGTERM? It would seem to be a one-liner.

[tdw-hughes]

Hi Euan, I can tell you how we worked around this:

in startup.cs:

Register some methods here:

        public void Configure(IApplicationBuilder app, IHostApplicationLifetime applicationLifetime, IWebHostEnvironment env, ILoggerFactory loggerFactory)
        {
            applicationLifetime.ApplicationStopping.Register(OnShutdown);
            applicationLifetime.ApplicationStarted.Register(OnStarted);

        ... etc. ...
        }

Add this code. We created a dummy PingController to use as an endpoint. It didn’t seem to matter whether the Controller returned successful or we got an authorisation error - it worked to make ASP register properly and then the expected shutdown calls are made.

        private void OnStarted()
        {
            // Force a request on the controller, as there is a bug in ASP.NET that doesn't shutdown services gracefully at service stop until at least one request received
            Task.Factory.StartNew(() =>
            {
                try
                {
                    var client = new HttpClient();
                    client.BaseAddress = new Uri("whatever path is to this service");
                    var result = client.SendAsync(new HttpRequestMessage(HttpMethod.Get, "api/Ping" )).Result;
                    Console.WriteLine($"Pinged an API controller to ensure shutdown will register correctly: {result.StatusCode}");
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            });
        }

        private void OnShutdown()
        {
            //noop - unless you have anything specific you need to do here.
        }