Fix DisableTelemetry not disabling metrics export

CHANGELOG.md

@@ -1,8 +1,7 @@
 # Changelog
 
 ## Unreleased
-- [Fix `TrackAvailability` ignoring user-specified `Timestamp` on `AvailabilityTelemetry`. The timestamp is now emitted as `microsoft.availability.testTimestamp` so downstream exporters can use the correct event time.](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3153)
-- [Added `netstandard2.0` target framework to `Microsoft.ApplicationInsights` package to support customers with shared libraries targeting netstandard2.0.](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3142)
+- [Fix `DisableTelemetry` not disabling metrics export: `OTEL_SDK_DISABLED` was set in IConfiguration too late (during options callback) after the OTel MeterProvider had already been constructed. Moved the check to a hosted service that runs before OpenTelemetry's TelemetryHostedService.](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3156)
 - [Fix `TelemetryClient.Context.Cloud.RoleName` set after construction now applies to all telemetry.](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3129)
 - [Fix bug where Debug/Trace level logs from TrackTrace API were not emitted to Application Insights](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3121)
 - [Fix Track API calls to not mutate the passed in dictionary if it is readonly](https://github.com/microsoft/ApplicationInsights-dotnet/pull/3119)

NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs

@@ -99,7 +99,7 @@
                         .WithApplicationInsights()
                         .UseApplicationInsightsTelemetry();
 
                     AddTelemetryConfigAndClient(services, VersionUtils.ExtensionLabelShimAspNetCore + VersionUtils.GetVersion(typeof(ApplicationInsightsExtensions)));
                     services.AddSingleton<IJavaScriptSnippet, JavaScriptSnippet>();
                     services.AddSingleton<JavaScriptSnippet>();
                 }
@@ -205,12 +205,6 @@
                 {
                     var serviceOptions = aiOptions.Value;
 
-                    // Set OTEL_SDK_DISABLED in configuration if DisableTelemetry is true
-                    if (telemetryConfig.DisableTelemetry)
-                    {
-                        config["OTEL_SDK_DISABLED"] = "true";
-                    }
-
                     if (!string.IsNullOrEmpty(telemetryConfig.StorageDirectory))
                     {
                         exporterOptions.StorageDirectory = telemetryConfig.StorageDirectory;

NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs

@@ -98,7 +98,7 @@
                             .WithApplicationInsights()
                             .UseApplicationInsightsTelemetry();
 
                     AddTelemetryConfigAndClient(services, VersionUtils.ExtensionLabelShimWorkerService + VersionUtils.GetVersion(typeof(ApplicationInsightsExtensions)));
                 }
 
                 return services;
@@ -200,12 +200,6 @@
                 {
                     var serviceOptions = aiOptions.Value;
 
-                    // Set OTEL_SDK_DISABLED in configuration if DisableTelemetry is true
-                    if (telemetryConfig.DisableTelemetry)
-                    {
-                        config["OTEL_SDK_DISABLED"] = "true";
-                    }
-
                     if (!string.IsNullOrEmpty(telemetryConfig.StorageDirectory))
                     {
                         exporterOptions.StorageDirectory = telemetryConfig.StorageDirectory;

NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs

@@ -19,6 +19,7 @@
 #endif
 
     using Microsoft.Extensions.Configuration;
+    using Microsoft.Extensions.Hosting;
     using Microsoft.Extensions.Logging;
     using Microsoft.Extensions.Options;
 
@@ -91,6 +92,14 @@ private static bool IsApplicationInsightsAdded(IServiceCollection services)
         private static void AddTelemetryConfigAndClient(IServiceCollection services, string extensionVersion)
         {
             services.AddOptions();
+
+            // Insert a hosted service at position 0 so it runs BEFORE OpenTelemetry's TelemetryHostedService.
+            // This ensures TelemetryConfiguration.DisableTelemetry is evaluated and OTEL_SDK_DISABLED is set
+            // in IConfiguration before the OTel SDK constructs its providers (which check OTEL_SDK_DISABLED).
+            if (!services.Any(d => d.ServiceType == typeof(IHostedService) && d.ImplementationType == typeof(DisableTelemetryInitializerHostedService)))
+            {
+                services.Insert(0, ServiceDescriptor.Singleton<IHostedService, DisableTelemetryInitializerHostedService>());
+            }
 
             // Register TelemetryConfiguration singleton with factory that creates it for DI scenarios
             // We use a factory to ensure skipDefaultBuilderConfiguration: true is passed

NETCORE/src/Shared/Extensions/DisableTelemetryInitializerHostedService.cs

@@ -0,0 +1,38 @@
+namespace Microsoft.Extensions.DependencyInjection
+{
+    using System;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.ApplicationInsights.Extensibility;
+    using Microsoft.Extensions.Configuration;
+    using Microsoft.Extensions.Hosting;
+
+    /// <summary>
+    /// A hosted service that runs before OpenTelemetry's TelemetryHostedService to set
+    /// OTEL_SDK_DISABLED in IConfiguration when TelemetryConfiguration.DisableTelemetry is true.
+    /// This ensures the OTel SDK sees the disabled flag before constructing providers.
+    /// </summary>
+    internal sealed class DisableTelemetryInitializerHostedService : IHostedService
+    {
+        private readonly IServiceProvider serviceProvider;
+
+        public DisableTelemetryInitializerHostedService(IServiceProvider serviceProvider)
+        {
+            this.serviceProvider = serviceProvider;
+        }
+
+        public Task StartAsync(CancellationToken cancellationToken)
+        {
+            var telemetryConfig = this.serviceProvider.GetService<TelemetryConfiguration>();
+            if (telemetryConfig != null && telemetryConfig.DisableTelemetry)
+            {
+                var config = this.serviceProvider.GetRequiredService<IConfiguration>();
+                config["OTEL_SDK_DISABLED"] = "true";
+            }
+
+            return Task.CompletedTask;
+        }
+
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+    }
+}

NETCORE/src/Shared/Shared.projitems

@@ -13,6 +13,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)ApplicationVersionResourceDetector.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\ApplicationInsightsExtensions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Extensions\ApplicationInsightsServiceOptions.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Extensions\DisableTelemetryInitializerHostedService.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Internals\ApplicationNameProvider.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Vendoring\OpenTelemetry.Resources.Azure\AppServiceResourceDetector.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Vendoring\OpenTelemetry.Resources.Azure\AzureContainerAppsResourceDetector.cs" />