How to propert kill ASP.NET Core application to restart docker container

Question

I have a simple ASP.NET Core Web API application that runs in docker container.

This app should process HTTP requests and consume events from Kafka. So, in Startup.Configure method I run dedicated thread with infinity loop to consume events.

public void Consume()
{
    Task.Factory.StartNew(async () =>
    {
        try
        {
            while (true)
            {
                var eventMsg = _consumer.Consume();
                await Handle(eventMsg);
            }
        }
        catch (Exception ex)
        {
            _consumer.Close();
                    // log error
            throw;
        }
    }, TaskCreationOptions.LongRunning);
}

Then in Startup

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseHsts();
            }

            app.UseAuthentication();
            app.UseMvc();

            var consumer = app.ApplicationServices.GetRequiredService<KafkaConsumer>();
            consumer.Consume();
        }

But when error occurs in loop I need to restart container with application. In simple application when I add throw; then it generate unhandled exception, close application and in a result container will be restarted. But in this case throw; didn't help, because it throw in background thread and I'm not waiting for result. I'm not waiting for result, because when I add

await consumer.Consume();

it stops all application and WebAPI not run.

How to handle this in proper way? If short, I need throw exception in background thread then close app to automatically restart container. I can't add Application.Exit to Consume method, because it is a library, and I can't change code.

Is there any other way to kill app from background thread?

Please let me know if I need to add more info before closing it.

Answer 1

This app should process HTTP requests and consume events from Kafka. So, in Startup.Configure method I run dedicated thread with infinity loop to consume events.

The proper way to run a background service on ASP.NET Core is to use Hosted Services. So your code would look like this:

public class KafkaConsumer : BackgroundService
{
  public KafkaConsumer()
  {
    _consumer = ...;
  }

  protected override Task ExecuteAsync(CancellationToken stoppingToken) => Task.Run(async () => 
  {
    try
    {
      while (true)
      {
        var eventMsg = _consumer.Consume();
        await Handle(eventMsg);
      }
    }
    catch (Exception ex)
    {
      _consumer.Close();
      ... // log error
      throw;
    }
  });
}

and it's registered in your startup class like this:

public void ConfigureServices(IServiceCollection services)
{
  services.AddHostedService<KafkaConsumer>();
}

But when error occurs in loop I need to restart container with application.

To do this, inject IHostApplicationLifetime and call StopApplication:

public class KafkaConsumer : BackgroundService
{
  private IHostApplicationLifetime _hostApplicationLifetime;

  public KafkaConsumer(IHostApplicationLifetime hostApplicationLifetime)
  {
    _hostApplicationLifetime = hostApplicationLifetime;
    _consumer = ...;
  }

  protected override Task ExecuteAsync(CancellationToken stoppingToken) => Task.Run(async () => 
  {
    try
    {
      while (true)
      {
        var eventMsg = _consumer.Consume();
        await Handle(eventMsg);
      }
    }
    catch (Exception ex)
    {
      _consumer.Close();
      ... // log error
      _hostApplicationLifetime.StopApplication();
      throw;
    }
  });
}