Make sure AkkaHostedService failures are always visible

src/Akka.Hosting.Tests/StartFailureSpec.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Threading.Tasks;
+using Akka.Actor;
+using FluentAssertions;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Xunit;
+using Xunit.Abstractions;
+using static FluentAssertions.FluentActions;
+
+namespace Akka.Hosting.Tests;
+
+public class StartFailureSpec
+{
+    private readonly ITestOutputHelper _output;
+
+    public StartFailureSpec(ITestOutputHelper output)
+    {
+        _output = output;
+    }
+
+    [Fact]
+    public async Task ShouldThrowWhenActorSystemFailedToStart()
+    {
+        // arrange
+        var host = new HostBuilder()
+            .ConfigureLogging(builder =>
+            {
+                builder.ClearProviders();
+                builder.AddProvider(new XUnitLoggerProvider(_output, LogLevel.Debug));
+            })
+            .ConfigureServices(services =>
+            {
+                services.AddAkka("MySys", (builder, provider) =>
+                {
+                    builder.AddStartup((_, _) => throw new TestException("BOOM"));
+                });
+            })
+            .Build();
+
+        await Awaiting(async () => await host.StartAsync()).Should()
+            .ThrowExactlyAsync<TestException>().WithMessage("BOOM");
+    }
+
+    private class TestException: Exception
+    {
+        public TestException(string? message) : base(message)
+        {
+        }
+    }
+}

src/Akka.Hosting/AkkaHostedService.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.ExceptionServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Akka.Actor;
@@ -74,8 +75,13 @@ async Task TerminationHook()
                 Logger.Log(LogLevel.Critical, ex, "Unable to start AkkaHostedService - shutting down application");
 
                 // resolve https://github.com/akkadotnet/Akka.Hosting/issues/470 - never allow failures to be silent
-                Console.WriteLine($"Unable to start AkkaHostedService due to [{ex}] - shutting down application");
-                HostApplicationLifetime?.StopApplication();
+                Console.WriteLine($"Unable to start AkkaHostedService - shutting down application.\nCause: {ex}");
+
+                // Best effort to perform a clean stop
+                var capturedException = ExceptionDispatchInfo.Capture(ex);
+                using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
+                await StopAsync(cts.Token);
+                capturedException.Throw();
             }
         }