Fix a regression in IHostedService startup order (#181)

Author: johnstairs

Makefile

@@ -38,7 +38,7 @@ az-login-from-host:
 	scripts/az-login-from-host.sh
 
 build-csharp:
-	find . -name *csproj | xargs -L 1 dotnet build
+	dotnet build server/tyger.sln
 
 build-go:
 	cd cli

server/Common/DependencyInjection/ServiceOrder.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Tyger.Common.DependencyInjection;
+
+public static class ServiceOrderHostApplicationBuilderExtensions
+{
+    /// <summary>
+    /// Adds a service descriptor to the IHostApplicationBuilder with a specified priority.
+    /// </summary>
+    /// <remarks>
+    /// If a service descriptor with the same service type already exists, the new service descriptor
+    /// will be inserted before the existing one if the new service's priority is higher. Otherwise, it will be added
+    /// to the end of the service collection. Services added outside of this method have priority 0.
+    /// </remarks>
+    public static IHostApplicationBuilder AddServiceWithPriority(this IHostApplicationBuilder builder, ServiceDescriptor serviceDescriptor, int priority)
+    {
+        builder.Properties[serviceDescriptor] = priority;
+        for (int i = 0; i < builder.Services.Count; i++)
+        {
+            var existingService = builder.Services[i];
+            if (existingService.ServiceType == serviceDescriptor.ServiceType)
+            {
+                var existingPriority = builder.Properties.TryGetValue(existingService, out var value) ? (int)value : 0;
+                if (priority > existingPriority)
+                {
+                    builder.Services.Insert(i, serviceDescriptor);
+                    return builder;
+                }
+            }
+        }
+
+        builder.Services.Add(serviceDescriptor);
+        return builder;
+    }
+}

server/ControlPlane/Buffers/Buffers.cs

@@ -7,6 +7,7 @@
 using Microsoft.Extensions.Primitives;
 using Microsoft.OpenApi.Models;
 using Tyger.Common.Api;
+using Tyger.Common.DependencyInjection;
 using Tyger.ControlPlane.Json;
 using Tyger.ControlPlane.Model;
 using Buffer = Tyger.ControlPlane.Model.Buffer;
@@ -35,7 +36,7 @@ public static void AddBuffers(this IHostApplicationBuilder builder)
                 {
                     builder.Services.AddSingleton<AzureBlobBufferProvider>();
                     builder.Services.AddSingleton<IBufferProvider>(sp => sp.GetRequiredService<AzureBlobBufferProvider>());
-                    builder.Services.Insert(0, ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<AzureBlobBufferProvider>())); // Other startup services depend on this, so we add it early.
+                    builder.AddServiceWithPriority(ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<AzureBlobBufferProvider>()), 10);
                     builder.Services.AddHealthChecks().AddCheck<AzureBlobBufferProvider>("buffers");
                 }
 

server/ControlPlane/Compute/Kubernetes/Kubernetes.cs

@@ -8,6 +8,7 @@
 using Microsoft.Extensions.Http.Resilience;
 using Microsoft.Extensions.Options;
 using Polly;
+using Tyger.Common.DependencyInjection;
 using Tyger.ControlPlane.Buffers;
 using Tyger.ControlPlane.Database;
 using Tyger.ControlPlane.Logging;
@@ -51,8 +52,7 @@ public static void AddKubernetes(this IHostApplicationBuilder builder)
             builder.Services.AddOptions<KubernetesApiOptions>().BindConfiguration("compute:kubernetes").ValidateDataAnnotations().ValidateOnStart();
 
             builder.Services.AddSingleton(sp => new LeaseManager(sp.GetRequiredService<Repository>(), "tyger-server-leader"));
-            builder.Services.Insert(0, ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<LeaseManager>())); // Other startup services depend on this, so we add it early.
-
+            builder.AddServiceWithPriority(ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<LeaseManager>()), 20);
             builder.Services.AddSingleton<KubernetesRunCreator>();
             builder.Services.AddSingleton<IRunCreator>(sp => sp.GetRequiredService<KubernetesRunCreator>());
             builder.Services.AddHostedService(sp => sp.GetRequiredService<KubernetesRunCreator>());

server/ControlPlane/Database/Database.cs

@@ -11,6 +11,7 @@
 using Npgsql;
 using Polly;
 using Polly.Retry;
+using Tyger.Common.DependencyInjection;
 using Tyger.ControlPlane.Compute.Kubernetes;
 using Tyger.ControlPlane.Database.Migrations;
 using Tyger.ControlPlane.Model;
@@ -105,10 +106,10 @@ public static void AddDatabase(this IHostApplicationBuilder builder)
         });
 
         builder.Services.AddSingleton<MigrationRunner>();
-        builder.Services.AddHostedService(sp => sp.GetRequiredService<MigrationRunner>());
+        builder.AddServiceWithPriority(ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<MigrationRunner>()), 200);
 
         builder.Services.AddSingleton<DatabaseVersions>();
-        builder.Services.AddHostedService(sp => sp.GetRequiredService<DatabaseVersions>());
+        builder.AddServiceWithPriority(ServiceDescriptor.Singleton<IHostedService>(sp => sp.GetRequiredService<DatabaseVersions>()), 100);
         builder.Services.AddHealthChecks().AddCheck<DatabaseVersions>("database");
     }