Stop health checks running until the underlying resource enters the running state.

playground/AzureFunctionsEndToEnd/AzureFunctionsEndToEnd.AppHost/appsettings.json

@@ -4,6 +4,7 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning",
       "Aspire.Hosting.Dcp": "Warning"
+
     }
   }
 }

playground/ProxylessEndToEnd/ProxylessEndToEnd.AppHost/appsettings.json

@@ -4,6 +4,7 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning",
       "Aspire.Hosting.Dcp": "Warning"
+
     }
   }
 }

playground/TestShop/TestShop.AppHost/appsettings.json

@@ -4,6 +4,7 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning",
       "Aspire.Hosting.Dcp": "Warning"
+
     }
   }
 }

playground/nats/Nats.AppHost/appsettings.json

@@ -0,0 +1,9 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning",
+      "Aspire.Hosting.Dcp": "Warning"
+    }
+  }
+}

playground/python/Python.AppHost/appsettings.json

@@ -4,6 +4,7 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning",
       "Aspire.Hosting.Dcp": "Warning"
+
     }
   }
 }

src/Aspire.Hosting/DistributedApplicationBuilder.cs

@@ -131,6 +131,10 @@ public DistributedApplicationBuilder(DistributedApplicationOptions options)
         _innerBuilder.Logging.AddFilter("Aspire.Hosting.Dashboard", LogLevel.Error);
         _innerBuilder.Logging.AddFilter("Grpc.AspNetCore.Server.ServerCallHandler", LogLevel.Error);
 
+        // This is to reduce log noise when we activate health checks for resources which may not yet be
+        // fully initialized. For example a database which is not yet created.
+        _innerBuilder.Logging.AddFilter("Microsoft.Extensions.Diagnostics.HealthChecks.DefaultHealthCheckService", LogLevel.None);
+
         // This is so that we can see certificate errors in the resource server in the console logs.
         // See: https://github.com/dotnet/aspire/issues/2914
         _innerBuilder.Logging.AddFilter("Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer", LogLevel.Warning);
@@ -162,11 +166,19 @@ public DistributedApplicationBuilder(DistributedApplicationOptions options)
         _innerBuilder.Services.AddHostedService<DistributedApplicationRunner>();
         _innerBuilder.Services.AddSingleton(options);
         _innerBuilder.Services.AddSingleton<ResourceNotificationService>();
-        _innerBuilder.Services.AddSingleton<IHealthCheckPublisher, ResourceNotificationHealthCheckPublisher>();
-        _innerBuilder.Services.AddSingleton<ResourceLoggerService>();
         _innerBuilder.Services.AddSingleton<IDistributedApplicationEventing>(Eventing);
         _innerBuilder.Services.AddHealthChecks();
 
+        // Healthchecks
+        _innerBuilder.Services.AddSingleton<IHealthCheckPublisher, ResourceNotificationHealthCheckPublisher>();
+        _innerBuilder.Services.AddHostedService<ResourceHealthCheckScheduler>();
+        _innerBuilder.Services.AddSingleton<ResourceLoggerService>();
+        _innerBuilder.Services.Configure<HealthCheckPublisherOptions>(options =>
+        {
+            // Disable health checks from running!
+            options.Predicate = (check) => false;
+        });
+
         if (ExecutionContext.IsRunMode)
         {
             // Dashboard

src/Aspire.Hosting/Health/ResourceHealthCheckScheduler.cs

@@ -0,0 +1,67 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Hosting.ApplicationModel;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Options;
+
+namespace Aspire.Hosting.Health;
+
+internal class ResourceHealthCheckScheduler(IOptions<HealthCheckPublisherOptions> healthCheckPublisherOptions, ResourceNotificationService resourceNotificationService, DistributedApplicationModel model) : BackgroundService, IHostedLifecycleService
+{
+    public Task StartedAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    public Task StartingAsync(CancellationToken cancellationToken)
+    {
+        // When we startup pre-populate the list of checks and set them
+        // all to false so we don't run any initially.
+        foreach (var resource in model.Resources)
+        {
+            UpdateCheckEnablement(resource, false);
+        }
+
+        healthCheckPublisherOptions.Value.Period = TimeSpan.FromSeconds(5);
+        healthCheckPublisherOptions.Value.Predicate = ShouldRunCheck;
+
+        return Task.CompletedTask;
+    }
+
+    private readonly Dictionary<string, bool> _checkEnablement = new();
+
+    private bool ShouldRunCheck(HealthCheckRegistration check)
+    {
+        // We don't run any health checks that aren't associated with a resource.
+        return _checkEnablement.TryGetValue(check.Name, out var enabled) ? enabled : false;
+    }
+
+    public Task StoppedAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    public Task StoppingAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var resourceEvents = resourceNotificationService.WatchAsync(stoppingToken);
+
+        await foreach (var resourceEvent in resourceEvents)
+        {
+            if (resourceEvent.Snapshot.State == KnownResourceStates.Running)
+            {
+                // Each time we receive an event that tells us that the resource is
+                // running we need to enable the health check annotation.
+                UpdateCheckEnablement(resourceEvent.Resource, true);
+            }
+        }
+    }
+
+    private void UpdateCheckEnablement(IResource resource, bool enabled)
+    {
+        if (resource.TryGetAnnotationsOfType<HealthCheckAnnotation>(out var annotations))
+        {
+            foreach (var annotation in annotations)
+            {
+                _checkEnablement[annotation.Key] = enabled;
+            }
+        }
+    }
+}

src/Aspire.Hosting/Health/ResourceNotificationHealthCheckPublisher.cs

@@ -14,8 +14,8 @@ public async Task PublishAsync(HealthReport report, CancellationToken cancellati
         {
             if (resource.TryGetAnnotationsOfType<HealthCheckAnnotation>(out var annotations))
             {
-                var resourceEntries = report.Entries.Where(e => annotations.Any(a => a.Key == e.Key));
-                var status = resourceEntries.All(e => e.Value.Status == HealthStatus.Healthy) ? HealthStatus.Healthy : HealthStatus.Unhealthy;
+                // Make sure every annotation is represented as health in the report, and if an entry is missing that means it is unhealthy.
+                var status = annotations.All(a => report.Entries.TryGetValue(a.Key, out var entry) && entry.Status == HealthStatus.Healthy) ? HealthStatus.Healthy : HealthStatus.Unhealthy;
 
                 await resourceNotificationService.PublishUpdateAsync(resource, s => s with
                 {