Add error handling for URL parameter resolution in external service

src/Aspire.Hosting/ExternalServiceBuilderExtensions.cs

@@ -105,9 +105,24 @@ private static IResourceBuilder<ExternalServiceResource> AddExternalServiceImpl(
                 if (uri is null)
                 {
                     // If the URI is not set, it means we are using a parameterized URL
-                    var url = resource.UrlParameter is null
-                            ? null
-                            : await resource.UrlParameter.GetValueAsync(ct).ConfigureAwait(false);
+                    string? url;
+                    try
+                    {
+                        url = resource.UrlParameter is null
+                                ? null
+                                : await resource.UrlParameter.GetValueAsync(ct).ConfigureAwait(false);
+                    }
+                    catch (Exception ex)
+                    {
+                        e.Logger.LogError(ex, "Failed to get value for URL parameter '{ParameterName}'", resource.UrlParameter?.Name);
+
+                        await e.Notifications.PublishUpdateAsync(resource, snapshot => snapshot with
+                        {
+                            State = KnownResourceStates.FailedToStart
+                        }).ConfigureAwait(false);
+
+                        return;
+                    }
 
                     if (!ExternalServiceResource.UrlIsValidForExternalService(url, out uri, out var message))
                     {

tests/Aspire.Hosting.Tests/ExternalServiceTests.cs

@@ -289,6 +289,87 @@ public void ExternalServiceUrlValidationHelper()
         Assert.Contains("absolute path must be \"/\"", pathMessage);
     }
 
+    [Fact]
+    public async Task ExternalServiceWithParameterGetValueAsyncErrorMarksAsFailedToStart()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create();
+
+        // Create a parameter with a broken value callback
+        var urlParam = builder.AddParameter("failing-url", () => throw new InvalidOperationException("Parameter resolution failed"));
+        var externalService = builder.AddExternalService("external", urlParam);
+
+        using var app = builder.Build();
+
+        // Start the app to trigger InitializeResourceEvent
+        var appStartTask = app.StartAsync();
+
+        // Wait for the resource to be marked as FailedToStart
+        var resourceEvent = await app.ResourceNotifications.WaitForResourceAsync(
+            externalService.Resource.Name,
+            e => e.Snapshot.State?.Text == KnownResourceStates.FailedToStart
+        ).DefaultTimeout();
+
+        // Verify the resource is in the correct state
+        Assert.Equal(KnownResourceStates.FailedToStart, resourceEvent.Snapshot.State?.Text);
+
+        await app.StopAsync();
+        await appStartTask; // Ensure start completes
+    }
+
+    [Fact]
+    public async Task ExternalServiceWithParameterInvalidUrlMarksAsFailedToStart()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create();
+
+        // Create a parameter that returns an invalid URL
+        var urlParam = builder.AddParameter("invalid-url", () => "invalid-url-not-absolute");
+        var externalService = builder.AddExternalService("external", urlParam);
+
+        using var app = builder.Build();
+
+        // Start the app to trigger InitializeResourceEvent
+        var appStartTask = app.StartAsync();
+
+        // Wait for the resource to be marked as FailedToStart
+        var resourceEvent = await app.ResourceNotifications.WaitForResourceAsync(
+            externalService.Resource.Name,
+            e => e.Snapshot.State?.Text == KnownResourceStates.FailedToStart
+        ).DefaultTimeout();
+
+        // Verify the resource is in the correct state
+        Assert.Equal(KnownResourceStates.FailedToStart, resourceEvent.Snapshot.State?.Text);
+
+        await app.StopAsync();
+        await appStartTask; // Ensure start completes
+    }
+
+    [Fact]
+    public async Task ExternalServiceWithValidParameterMarksAsRunning()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create();
+
+        // Create a parameter that returns a valid URL
+        var urlParam = builder.AddParameter("valid-url", () => "https://example.com/");
+        var externalService = builder.AddExternalService("external", urlParam);
+
+        using var app = builder.Build();
+
+        // Start the app to trigger InitializeResourceEvent
+        var appStartTask = app.StartAsync();
+
+        // Wait for the resource to be marked as Running
+        var resourceEvent = await app.ResourceNotifications.WaitForResourceAsync(
+            externalService.Resource.Name,
+            e => e.Snapshot.State?.Text == KnownResourceStates.Running
+        ).DefaultTimeout();
+
+        // Verify the resource is in the correct state
+        Assert.Equal(KnownResourceStates.Running, resourceEvent.Snapshot.State?.Text);
+
+        await app.StopAsync();
+        await appStartTask; // Ensure start completes
+    }
+
     private sealed class TestProject : IProjectMetadata
     {
         public string ProjectPath => "testproject";