---
title: "BackgroundService exceptions now propagate in .NET 11"
description: "Here's a bug that lived in .NET for over four years <sup>As in: Reported over 4 years ago</sup>. If your `BackgroundService` threw an exception after its first `await`, your host would catch it, log a critical message, and then exit cleanly with **exit code 0**.\n\nSo everyone would think it terminated successfully. That got fixed!"
updated: 2026-05-10
tags: [".NET 11", ".NET", "ASP.NET"]
canonical: "https://steven-giesel.com/blogPost/00fcb870-6bf7-4f97-824f-8eab1b8838be/backgroundservice-exceptions-now-propagate-in-net-11"
---

# BackgroundService exceptions now propagate in .NET 11

Here's a bug that lived in .NET for over four years <sup>As in: Reported over 4 years ago</sup>. If your `BackgroundService` threw an exception after its first `await`, your host would catch it, log a critical message, and then exit cleanly with **exit code 0**.

So everyone would think it terminated successfully. That got fixed!

## The Problem
Consider this worker:

```csharp
public class Worker : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await Task.Delay(TimeSpan.FromSeconds(1), stoppingToken);
        throw new Exception("something went wrong");
    }
}
```

Before .NET 11, the output looked like this:

```
crit: Microsoft.Extensions.Hosting.Internal.Host[10]
      The HostOptions.BackgroundServiceExceptionBehavior is configured to StopHost.
      A BackgroundService has thrown an unhandled exception, and the IHost instance is stopping.
      ...
      System.Exception: something went wrong
info: Microsoft.Hosting.Lifetime[0]
      Application is shutting down...

Process finished with exit code 0.  ? !!
```

It get's logged as critical error, but the exit code is still 0.

## Why did it behave like this?

~~This is one of those cases where the bug lives at the boundary of sync and async. Everything depends on whether the exception is thrown *before or after* the first `await`.~~ 
EDIT: As [@StephenCleary](https://github.com/StephenCleary) pointed out in the comments the sole existing of `async` make the issue arise. The following part is wrong, but I keep it for transparency. Therefore: `async` is the root cause, doesn't matter if the exception is thrown before or after the async boundary.

**Before the first `await`:**
```csharp
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    throw new Exception(); // no await yet
}
```
The exception propagates synchronously during host startup and crashes the process — exit code 134. Correct behavior.

**After the first `await`**
```csharp
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    await Task.Delay(1000, stoppingToken); // crosses the boundary
    throw new Exception();
}
```
By this point, the host has already started. The exception gets caught by `TryExecuteBackgroundServiceAsync` deep inside the hosting infrastructure, logged as critical, and then the host initiates a graceful shutdown. Graceful shutdown = exit code 0.

The root cause is that `host.RunAsync()` returns `Task` (not `Task<int>`), and there was no mechanism for a failing background service to signal that the *process* should exit with an error code. It just... didn't.

## The fix in .NET 11

PR [#124863](https://github.com/dotnet/runtime/pull/124863) makes `IHost.RunAsync()` and `IHost.StopAsync()` propagate the `BackgroundService` exception rather than swallowing it. Now you get:

```
crit: Microsoft.Extensions.Hosting.Internal.Host[10]
      ...
      System.Exception: something went wrong

Unhandled exception. System.Exception: something went wrong
   at Worker.ExecuteAsync(...)

Process finished with exit code 134. (or 1 on Windows)
```

## What if you want the old behavior?

You can opt out by setting the exception behavior to `Ignore`:

```csharp
services.Configure<HostOptions>(options =>
{
    options.BackgroundServiceExceptionBehavior = BackgroundServiceExceptionBehavior.Ignore;
});
```

## `IHostedService`

Just for completeness: If you implement the `IHostedService` yourself, it works as you expect:

```csharp
public class FailingHostedService : IHostedService
{
    public async Task StartAsync(CancellationToken cancellationToken)
    {
        throw new NotImplementedException();
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        throw new NotImplementedException();
    }
}
```

The described stuff above is referring to `HostedService` which is a wrapper around `IHostedService`.

## Resources

The original issue: [https://github.com/dotnet/runtime/issues/67146](https://github.com/dotnet/runtime/issues/67146)


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