azure-webjob-host

Provides shutdown detection for your azure webjob without taking the whole Azure WebJobs SDK.

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Package	Version
AzureWebjobHost

Background

The way Azure notifies a WebJob process it's about to be stopped is by placing (creating) a file at a path defined by the environment variable WEBJOBS_SHUTDOWN_FILE. This means Azure is going to stop your process in 5 seconds time (although that time is configurable). If you to be able to react, so that you can gracefully shutdown, you'd better listen for it.

One way to do this is to use the Azure WebJobs SDK.

But if you don't want to take that dependency, this is a lighter weight, less opinionated alternative.

How to use it

This library uses the Microsoft.Extensions.Hosting pattern to provide shutdown notifications to your continuous service. Just provide your class as a IHostedService to our ServiceHost

IHostedService myService = new MyService();

using (var host = new ServiceHostBuilder().HostService(myService))
{
    await host.RunAsync(default);
}

// Found in Microsoft.Extensions.Hosting
// public interface IHostedService
// {
//    Task StartAsync(CancellationToken cancellationToken);
//    Task StopAsync(CancellationToken cancellationToken);
// }

Or, if you just want to run a Task instead of a IHostedService, use the JobHost instead. Be sure to provide a Task that will act on the cancellation request.

async Task DoSomething(CancellationToken cancellationToken)
        {
          if (cancellationToken.IsCancellationRequested) return;

          for (int i = 0; i < 100; i++)
          {
              if (cancellationToken.IsCancellationRequested) return;
              await Task.Delay(100);
              Console.WriteLine("hello world");
          }
        };

using (var host = new JobHostBuilder().Build())
{
    await host.RunAsync(DoSomething);
    // var result = host.RunAsync(ReturnSomething) <- Also available with return values 
}

What happens if the host detects a shutdown

If the Azure web job detects a shutdown while your code is executing the ServiceHost will call StopAsync on your service. If you're using the JobService instead, that will cancel the token that was provided to your method

In the case of a WEBJOBS_SHUTDOWN_FILE shutdown your code will have 5 seconds (configurable in Azure) to gracefully exit.

There are other types of exit however. The hosts are also listening for AppDomain.CurrentDomain.ProcessExit and Console.CancelKeyPress. Your code will be notified in the same way, and the host will attempt to block these types of shutdowns for up to 4 seconds while your code inside the host.RunAsync exits.

Note, that because this code it intended to allow your whole process to exit, but only directly tries to block shutdown while code inside the host is running, it's best to put the hosting code as close to the top of your application as possible. This is a "framework level concern", not something to mix in with your application code. I place it at the top of Main in my WebJob console apps.