Wait for dashboard to be healthy before returning URL via RPC.

src/Aspire.Hosting/Aspire.Hosting.csproj

@@ -21,6 +21,7 @@
     <Compile Include="$(SharedDir)Model\KnownRelationshipTypes.cs" Link="Dashboard\KnownRelationshipTypes.cs" />
     <Compile Include="$(SharedDir)IConfigurationExtensions.cs" Link="Utils\IConfigurationExtensions.cs" />
     <Compile Include="$(SharedDir)KnownFormats.cs" Link="Utils\KnownFormats.cs" />
+    <Compile Include="$(SharedDir)KnownHealthCheckNames.cs" Link="Utils\KnownHealthCheckNames.cs" />
     <Compile Include="$(SharedDir)KnownResourceNames.cs" Link="Utils\KnownResourceNames.cs" />
     <Compile Include="$(SharedDir)KnownConfigNames.cs" Link="Utils\KnownConfigNames.cs" />
     <Compile Include="$(SharedDir)PathNormalizer.cs" Link="Utils\PathNormalizer.cs" />

src/Aspire.Hosting/Backchannel/AppHostRpcTarget.cs

@@ -21,7 +21,8 @@ internal class AppHostRpcTarget(
     IServiceProvider serviceProvider,
     IDistributedApplicationEventing eventing,
     PublishingActivityProgressReporter activityReporter,
-    IHostApplicationLifetime lifetime
+    IHostApplicationLifetime lifetime,
+    DistributedApplicationOptions options
     ) 
 {
     public async IAsyncEnumerable<(string Id, string StatusText, bool IsComplete, bool IsError)> GetPublishingActivitiesAsync([EnumeratorCancellation]CancellationToken cancellationToken)
@@ -101,6 +102,25 @@ public Task<long> PingAsync(long timestamp, CancellationToken cancellationToken)
 
     public Task<(string BaseUrlWithLoginToken, string? CodespacesUrlWithLoginToken)> GetDashboardUrlsAsync()
     {
+        return GetDashboardUrlsAsync(CancellationToken.None);
+    }
+
+    public async Task<(string BaseUrlWithLoginToken, string? CodespacesUrlWithLoginToken)> GetDashboardUrlsAsync(CancellationToken cancellationToken)
+    {
+        if (!options.DashboardEnabled)
+        {
+            logger.LogError("Dashboard URL requested but dashboard is disabled.");
+            throw new InvalidOperationException("Dashboard URL requested but dashboard is disabled.");
+        }
+
+        // Wait for the dashboard to be healthy before we return the URL. This is to avoid
+        // a race condition when using Codespaces or devcontainers where the dashboard URL
+        // is displayed before the dashboard port forwarding is actually configured. It is
+        // also a point of friction to show the URL before the dashboard is ready to be used
+        // when using Devcontainers/Codespaces because people think that something isn't working
+        // when in fact they just need to refresh the page.
+        await resourceNotificationService.WaitForResourceHealthyAsync(KnownResourceNames.AspireDashboard, cancellationToken).ConfigureAwait(false);
+
         var dashboardOptions = serviceProvider.GetService<IOptions<DashboardOptions>>();
 
         if (dashboardOptions is null)
@@ -122,11 +142,11 @@ public Task<long> PingAsync(long timestamp, CancellationToken cancellationToken)
 
         if (baseUrlWithLoginToken == codespacesUrlWithLoginToken)
         {
-            return Task.FromResult<(string, string?)>((baseUrlWithLoginToken, null));
+            return (baseUrlWithLoginToken, null);
         }
         else
         {
-            return Task.FromResult((baseUrlWithLoginToken, codespacesUrlWithLoginToken));
+            return (baseUrlWithLoginToken, codespacesUrlWithLoginToken);
         }
     }
 

src/Aspire.Hosting/Dashboard/DashboardLifecycleHook.cs

@@ -127,7 +127,6 @@ private void AddDashboardResource(DistributedApplicationModel model)
         nameGenerator.EnsureDcpInstancesPopulated(dashboardResource);
 
         ConfigureAspireDashboardResource(dashboardResource);
-
         // Make the dashboard first in the list so it starts as fast as possible.
         model.Resources.Insert(0, dashboardResource);
     }
@@ -179,6 +178,7 @@ private void ConfigureAspireDashboardResource(IResource dashboardResource)
         dashboardResource.Annotations.Add(new ResourceSnapshotAnnotation(snapshot));
 
         dashboardResource.Annotations.Add(new EnvironmentCallbackAnnotation(ConfigureEnvironmentVariables));
+        dashboardResource.Annotations.Add(new HealthCheckAnnotation(KnownHealthCheckNames.DasboardHealthCheck));
     }
 
     internal async Task ConfigureEnvironmentVariables(EnvironmentCallbackContext context)

src/Aspire.Hosting/DistributedApplicationBuilder.cs

@@ -19,6 +19,7 @@
 using Aspire.Hosting.Lifecycle;
 using Aspire.Hosting.Orchestrator;
 using Aspire.Hosting.Publishing;
+using Aspire.Hosting.Utils;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
@@ -331,6 +332,20 @@ public DistributedApplicationBuilder(DistributedApplicationOptions options)
                 _innerBuilder.Services.AddLifecycleHook<DashboardLifecycleHook>();
                 _innerBuilder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<DashboardOptions>, ConfigureDefaultDashboardOptions>());
                 _innerBuilder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IValidateOptions<DashboardOptions>, ValidateDashboardOptions>());
+
+                // Dashboard health check.
+                _innerBuilder.Services.AddHealthChecks().AddUrlGroup(sp => {
+
+                    var dashboardOptions = sp.GetRequiredService<IOptions<DashboardOptions>>().Value;
+                    if (StringUtils.TryGetUriFromDelimitedString(dashboardOptions.DashboardUrl, ";", out var firstDashboardUrl))
+                    {
+                        return firstDashboardUrl;
+                    }
+                    else
+                    {
+                        throw new DistributedApplicationException($"The dashboard resource '{KnownResourceNames.AspireDashboard}' does not have endpoints.");
+                    }
+                }, KnownHealthCheckNames.DasboardHealthCheck);
             }
 
             if (options.EnableResourceLogging)

src/Shared/KnownHealthCheckNames.cs

@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Aspire;
+
+internal static class KnownHealthCheckNames
+{
+    /// <summary>
+    /// Common name for dashboard health check.
+    /// </summary>
+    public const string DasboardHealthCheck = "aspire_dashboard_check";
+}