[WIP] Extend the Aspire Dashboard to reflect AppHost topology and publish an Azure Monitor Health Model

Aspire.slnx

@@ -101,6 +101,7 @@
     <Project Path="src/Aspire.Hosting.Azure.EventHubs/Aspire.Hosting.Azure.EventHubs.csproj" />
     <Project Path="src/Aspire.Hosting.Azure.FrontDoor/Aspire.Hosting.Azure.FrontDoor.csproj" />
     <Project Path="src/Aspire.Hosting.Azure.Functions/Aspire.Hosting.Azure.Functions.csproj" />
+    <Project Path="src/Aspire.Hosting.Azure.HealthModels/Aspire.Hosting.Azure.HealthModels.csproj" />
     <Project Path="src/Aspire.Hosting.Azure.KeyVault/Aspire.Hosting.Azure.KeyVault.csproj" />
     <Project Path="src/Aspire.Hosting.Azure.Kubernetes/Aspire.Hosting.Azure.Kubernetes.csproj" />
     <Project Path="src/Aspire.Hosting.Azure.Kusto/Aspire.Hosting.Azure.Kusto.csproj" />
@@ -286,6 +287,10 @@
   <Folder Name="/playground/HealthChecks/">
     <Project Path="playground/HealthChecks/HealthChecksSandbox.AppHost/HealthChecksSandbox.AppHost.csproj" />
   </Folder>
+  <Folder Name="/playground/HealthModel/">
+    <Project Path="playground/HealthModel/HealthModel.Metrics/HealthModel.Metrics.csproj" />
+    <Project Path="playground/HealthModel/HealthModelSandbox.AppHost/HealthModelSandbox.AppHost.csproj" />
+  </Folder>
   <Folder Name="/playground/kafka/">
     <Project Path="playground/kafka/Consumer/Consumer.csproj" />
     <Project Path="playground/kafka/KafkaBasic.AppHost/KafkaBasic.AppHost.csproj" />

playground/HealthModel/.vscode/launch.json

@@ -0,0 +1,11 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Run AppHost",
+            "type": "aspire",
+            "request": "launch",
+            "program": "${workspaceFolder}"
+        }
+    ]
+}

playground/HealthModel/HealthModel.Metrics/HealthModel.Metrics.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>$(DefaultTargetFramework)</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="..\HealthModelScenario.cs" Link="HealthModelScenario.cs" />
+    <!-- The linked scenario also compiles in non-web projects with explicit DI imports. -->
+    <Using Remove="Microsoft.Extensions.DependencyInjection" />
+  </ItemGroup>
+
+</Project>

playground/HealthModel/HealthModel.Metrics/HealthModelMetrics.cs

@@ -0,0 +1,63 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Globalization;
+using System.Text;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+namespace HealthModelPlayground;
+
+internal static class HealthModelMetrics
+{
+    public const string ContentType = "text/plain; version=0.0.4; charset=utf-8";
+
+    public static string Format(HealthReport report, IEnumerable<HealthModelScenarioResource> resources)
+    {
+        var output = new StringBuilder();
+        output.Append("# HELP aspire_health_status Simulated resource health: 0 = Unhealthy, 1 = Degraded, 2 = Healthy.\n");
+        output.Append("# TYPE aspire_health_status gauge\n");
+
+        foreach (var resource in resources.OrderBy(resource => resource.Name, StringComparer.Ordinal))
+        {
+            // An absent check is no data, even if the scenario's expected status is Healthy.
+            // In particular, do not use the aggregate report status for an individual resource.
+            if (report.Entries.TryGetValue(resource.HealthCheckName, out var entry))
+            {
+                AppendSample(output, resource.Name, resource.HealthCheckName, entry.Status);
+            }
+
+            // These entities run inside this serving process, rather than representing real databases.
+            AppendSample(output, resource.Name, "resource-state", HealthStatus.Healthy);
+        }
+
+        return output.ToString();
+    }
+
+    private static void AppendSample(StringBuilder output, string resourceName, string healthCheck, HealthStatus status)
+    {
+        output.Append("aspire_health_status{resource_name=\"");
+        AppendLabelValue(output, resourceName);
+        output.Append("\",health_check=\"");
+        AppendLabelValue(output, healthCheck);
+        output.Append("\",replica_index=\"1\"} ");
+        output.Append(((int)status).ToString(CultureInfo.InvariantCulture));
+        output.Append('\n');
+    }
+
+    private static void AppendLabelValue(StringBuilder output, string value)
+    {
+        // A label such as api"\name<LF>next is written as api\"\\name\nnext.
+        // Prometheus text format escapes backslashes, quotes, and line feeds:
+        // https://prometheus.io/docs/instrumenting/exposition_formats/#text-format-details
+        foreach (var character in value)
+        {
+            output.Append(character switch
+            {
+                '\\' => "\\\\",
+                '"' => "\\\"",
+                '\n' => "\\n",
+                _ => character.ToString()
+            });
+        }
+    }
+}

playground/HealthModel/HealthModel.Metrics/Program.cs

@@ -0,0 +1,21 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using HealthModelPlayground;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+var builder = WebApplication.CreateBuilder(args);
+HealthModelScenario.AddHealthChecks(builder.Services);
+
+var app = builder.Build();
+
+app.MapGet("/metrics", async (HealthCheckService healthChecks, CancellationToken cancellationToken) =>
+{
+    var report = await healthChecks.CheckHealthAsync(cancellationToken);
+    return Results.Text(HealthModelMetrics.Format(report, HealthModelScenario.Resources), HealthModelMetrics.ContentType);
+});
+
+// Process liveness is independent of the intentionally degraded and unhealthy simulated resources.
+app.MapGet("/alive", () => Results.Text("Alive\n", "text/plain"));
+
+app.Run();

playground/HealthModel/HealthModelSandbox.AppHost/AppHost.cs

@@ -0,0 +1,131 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#pragma warning disable ASPIREAZUREHEALTH001
+
+using Aspire.Hosting.Eventing;
+using Aspire.Hosting.Lifecycle;
+using HealthModelPlayground;
+
+// Playground for the health model and the resource graph.
+//
+// The topology below is a strict tree: every resource has exactly one parent, and nothing is shared between
+// branches. That is deliberate. A shared dependency turns the model into a graph, which is legitimate but
+// makes it much harder to see at a glance whether health is rolling up correctly, because a single unhealthy
+// leaf lights up several unrelated-looking paths at once.
+//
+//   storefront                        (Healthy)   web front end
+//   ├── checkout-api                  (Healthy)
+//   │   ├── orders-db-server          (Healthy)
+//   │   │   └── orders-db             (Healthy)   child of its server
+//   │   └── payments-gateway          (Degraded)  <- degrades the checkout branch
+//   ├── catalog-api                   (Healthy)
+//   │   ├── catalog-db-server         (Healthy)
+//   │   │   └── catalog-db            (Healthy)   child of its server
+//   │   └── search-index              (Unhealthy) <- fails the catalog branch
+//   └── identity-api                  (Healthy)   fully healthy branch
+//       └── identity-cache            (Healthy)
+//
+// Only two resources are anything other than healthy, so every other colour in the graph has been
+// inherited. The expected result once everything has started:
+//
+//   storefront    Unhealthy  (worst of its branches, via catalog-api -> search-index)
+//   checkout-api  Degraded   (via payments-gateway)
+//   catalog-api   Unhealthy  (via search-index)
+//   identity-api  Healthy    (nothing unhealthy underneath it)
+
+var builder = DistributedApplication.CreateBuilder(args);
+
+HealthModelScenario.AddHealthChecks(builder.Services);
+var resources = HealthModelScenario.Resources.ToDictionary(resource => resource.Name, AddTestResource, StringComparer.Ordinal);
+foreach (var resource in HealthModelScenario.Resources)
+{
+    if (resource.ParentName is { } parent)
+    {
+        resources[resource.Name].WithParentRelationship(resources[parent]);
+    }
+    foreach (var dependency in resource.Dependencies)
+    {
+        resources[resource.Name].WithReferenceRelationship(resources[dependency]);
+    }
+}
+
+if (builder.ExecutionContext.IsPublishMode)
+{
+    builder.AddAzureContainerAppEnvironment("azure");
+    var health = builder.AddAzureHealthModel("health", "aspire-healthmodel.json");
+    var metrics = builder.AddProject<Projects.HealthModel_Metrics>("health-metrics")
+        .WithHttpEndpoint(name: "http", targetPort: 8080)
+        .WithHttpHealthCheck("/alive")
+        .PublishAsAzureContainerApp((_, app) =>
+        {
+            app.Template.Scale.MinReplicas = 1;
+            app.Template.Scale.MaxReplicas = 1;
+        });
+
+    builder.AddAzureContainerAppsHealthModelCollector("health-collector", health, metrics.GetEndpoint("http"));
+}
+else
+{
+    builder.Services.TryAddEventingSubscriber<TestResourceLifecycle>();
+}
+
+#if !SKIP_DASHBOARD_REFERENCE
+// This project is only added in playground projects to support development/debugging
+// of the dashboard. It is not required in end developer code. Comment out this code
+// or build with `/p:SkipDashboardReference=true`, to test end developer
+// dashboard launch experience, Refer to Directory.Build.props for the path to
+// the dashboard binary (defaults to the Aspire.Dashboard bin output in the
+// artifacts dir).
+if (builder.ExecutionContext.IsRunMode)
+{
+    builder.AddProject<Projects.Aspire_Dashboard>(KnownResourceNames.AspireDashboard);
+}
+#endif
+
+builder.Build().Run();
+
+IResourceBuilder<TestResource> AddTestResource(HealthModelScenarioResource resource)
+{
+    return builder
+        .AddResource(new TestResource(resource.Name))
+        .WithHealthCheck(resource.HealthCheckName)
+        .WithInitialState(new()
+        {
+            ResourceType = "Test Resource",
+            State = "Starting",
+            Properties = [],
+        })
+        .ExcludeFromManifest();
+}
+
+internal sealed class TestResource(string name) : Resource(name), IResourceWithEndpoints;
+
+/// <summary>
+/// Moves the test resources to the running state shortly after startup.
+/// </summary>
+/// <remarks>
+/// The delay is intentional. It leaves the resources in an unknown state for long enough to see that a
+/// starting resource does not colour the graph, which is the behaviour that keeps the model from flashing
+/// red every time the app host boots.
+/// </remarks>
+internal sealed class TestResourceLifecycle(ResourceNotificationService notificationService) : IDistributedApplicationEventingSubscriber
+{
+    public async Task OnBeforeStartAsync(BeforeStartEvent @event, CancellationToken cancellationToken)
+    {
+        await Task.Delay(TimeSpan.FromSeconds(3), cancellationToken);
+
+        // Keep startup work owned by the lifecycle event so cancellation and publication failures are
+        // observed instead of escaping from fire-and-forget tasks after the AppHost has stopped.
+        await Task.WhenAll(@event.Model.Resources.OfType<TestResource>().Select(resource =>
+            notificationService.PublishUpdateAsync(
+                resource,
+                state => state with { State = new("Running", "success") })));
+    }
+
+    public Task SubscribeAsync(IDistributedApplicationEventing eventing, DistributedApplicationExecutionContext executionContext, CancellationToken cancellationToken)
+    {
+        eventing.Subscribe<BeforeStartEvent>(OnBeforeStartAsync);
+        return Task.CompletedTask;
+    }
+}

playground/HealthModel/HealthModelSandbox.AppHost/HealthModelSandbox.AppHost.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>$(DefaultTargetFramework)</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsAspireHost>true</IsAspireHost>
+    <UserSecretsId>0e5a0d0e-5b1c-4d0a-9d5f-2c4b6a8f1e73</UserSecretsId>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <AspireProjectOrPackageReference Include="Aspire.Hosting.AppHost" />
+    <AspireProjectOrPackageReference Include="Aspire.Hosting.Azure.HealthModels" />
+    <ProjectReference Include="..\HealthModel.Metrics\HealthModel.Metrics.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Compile Include="..\..\KnownResourceNames.cs" Link="KnownResourceNames.cs" />
+    <Compile Include="..\HealthModelScenario.cs" Link="HealthModelScenario.cs" />
+    <None Update="aspire-healthmodel.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+</Project>

playground/HealthModel/HealthModelSandbox.AppHost/Properties/launchSettings.json

@@ -0,0 +1,36 @@
+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "https://HealthModel.dev.localhost:17420;http://HealthModel.dev.localhost:15320",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "DOTNET_ENVIRONMENT": "Development"
+      }
+    },
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "applicationUrl": "http://HealthModel.dev.localhost:15320",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "DOTNET_ENVIRONMENT": "Development"
+      }
+    },
+    "generate-manifest": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "dotnetRunMessages": true,
+      "commandLineArgs": "--publisher manifest --output-path aspire-manifest.json",
+      "applicationUrl": "http://HealthModel.dev.localhost:16320",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "DOTNET_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

playground/HealthModel/HealthModelSandbox.AppHost/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

playground/HealthModel/HealthModelSandbox.AppHost/appsettings.json

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