Adds telemetry pipeline

Microsoft.FeatureManagement.sln

@@ -19,7 +19,9 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ConsoleApp", "examples\Cons
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TargetingConsoleApp", "examples\TargetingConsoleApp\TargetingConsoleApp.csproj", "{6558C21E-CF20-4278-AA08-EB9D1DF29D66}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "RazorPages", "examples\RazorPages\RazorPages.csproj", "{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RazorPages", "examples\RazorPages\RazorPages.csproj", "{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.FeatureManagement.Telemetry.ApplicationInsights", "src\Microsoft.FeatureManagement.Telemetry.ApplicationInsights\Microsoft.FeatureManagement.Telemetry.ApplicationInsights.csproj", "{0ADB5CFC-D3FA-48E5-910A-51770C8E608C}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -55,6 +57,10 @@ Global
 		{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{BA29A1BB-81D5-4EB1-AF37-6ECF64AF27E2}.Release|Any CPU.Build.0 = Release|Any CPU
+		{0ADB5CFC-D3FA-48E5-910A-51770C8E608C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0ADB5CFC-D3FA-48E5-910A-51770C8E608C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0ADB5CFC-D3FA-48E5-910A-51770C8E608C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0ADB5CFC-D3FA-48E5-910A-51770C8E608C}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

examples/AppInsightsWithEvaluationData/AppInsightsWithEvaluationData.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.ApplicationInsights.AspNetCore" Version="2.21.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.FeatureManagement.AspNetCore\Microsoft.FeatureManagement.AspNetCore.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.FeatureManagement.Telemetry.ApplicationInsights\Microsoft.FeatureManagement.Telemetry.ApplicationInsights.csproj" />
+  </ItemGroup>
+
+</Project>

src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/Microsoft.FeatureManagement.Telemetry.ApplicationInsights.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>netstandard2.0;netcoreapp3.1;net5.0;net6.0</TargetFrameworks>
+    <SignAssembly>true</SignAssembly>
+    <DelaySign>false</DelaySign>
+    <AssemblyOriginatorKeyFile>..\..\build\Microsoft.FeatureManagement.snk</AssemblyOriginatorKeyFile>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.ApplicationInsights" Version="2.21.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Microsoft.FeatureManagement\Microsoft.FeatureManagement.csproj" />
+  </ItemGroup>
+
+</Project>

src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/ServiceCollectionExtensions.cs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+namespace Microsoft.FeatureManagement.Telemetry.ApplicationInsights
+{
+    /// <summary>
+    /// Extensions used to add feature management publisher functionality.
+    /// </summary>
+    public static class ServiceCollectionExtensions
+    {
+        /// <summary>
+        /// Adds an event publisher that publishes feature evaluation events to Application Insights.
+        /// </summary>
+        /// <param name="services">The service collection that feature management services are added to.</param>
+        /// <returns>The <see cref="IServiceCollection"/> that was given as a parameter, with the publisher added.</returns>
+        public static IServiceCollection AddFeatureManagementTelemetryPublisherApplicationInsights(this IServiceCollection services)
+        {
+            //
+            // Add required services
+            services.TryAddSingleton<ITelemetryPublisher, TelemetryPublisherApplicationInsights>();
+
+            return services;
+        }
+    }
+}

src/Microsoft.FeatureManagement.Telemetry.ApplicationInsights/TelemetryPublisherApplicationInsights.cs

@@ -0,0 +1,64 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.ApplicationInsights;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.FeatureManagement.Telemetry.ApplicationInsights
+{
+    /// <summary>
+    /// Used to publish data from evaluation events to Application Insights
+    /// </summary>
+    public class TelemetryPublisherApplicationInsights : ITelemetryPublisher
+    {
+        private readonly string _eventName = "FeatureEvaluation";
+        private readonly TelemetryClient _telemetryClient;
+
+        public TelemetryPublisherApplicationInsights(TelemetryClient telemetryClient)
+        {
+            _telemetryClient = telemetryClient;
+        }
+
+        /// <summary>
+        /// Publishes a custom event to Application Insights using data from the given evaluation event.
+        /// </summary>
+        /// <param name="evaluationEvent"> The event to publish.</param>
+        /// <param name="cancellationToken"> A cancellation token.</param>
+        /// <returns>Returns a ValueTask that represents the asynchronous operation</returns>
+        public ValueTask PublishEvent(EvaluationEvent evaluationEvent, CancellationToken cancellationToken)
+        {
+            FeatureDefinition featureDefinition = evaluationEvent.FeatureDefinition;
+
+            Dictionary<string, string> properties = new Dictionary<string, string>()
+            {
+                { "FeatureName", featureDefinition.Name },
+                { "IsEnabled", evaluationEvent.IsEnabled.ToString() }
+            };
+
+            if (featureDefinition.ETag != null)
+            {
+                properties.Add("ETag", featureDefinition.ETag);
+            }
+
+            if (featureDefinition.Label != null)
+            {
+                properties.Add("Label", featureDefinition.Label);
+            }
+
+            if (featureDefinition.Tags != null)
+            {
+                foreach (KeyValuePair<string, string> kvp in featureDefinition.Tags)
+                {
+                    properties["Tags." + kvp.Key] = kvp.Value;
+                }
+            }
+
+            _telemetryClient.TrackEvent(_eventName, properties);
+
+
+            return new ValueTask();
+        }
+    }
+}

src/Microsoft.FeatureManagement/ConfigurationFeatureDefinitionProvider.cs

@@ -135,6 +135,10 @@ We support
             */
 
             RequirementType requirementType = RequirementType.Any;
+            string label = null;
+            string eTag = null;
+            bool enableTelemetry = false;
+            IReadOnlyDictionary<string, string> tags = null;
 
             var enabledFor = new List<FeatureFilterConfiguration>();
 
@@ -167,7 +171,7 @@ We support
                 if (!string.IsNullOrEmpty(rawRequirementType) && !Enum.TryParse(rawRequirementType, ignoreCase: true, out requirementType))
                 {
                     throw new FeatureManagementException(
-                        FeatureManagementError.InvalidConfigurationSetting, 
+                        FeatureManagementError.InvalidConfigurationSetting,
                         $"Invalid requirement type '{rawRequirementType}' for feature '{configurationSection.Key}'.");
                 }
 
@@ -187,13 +191,26 @@ We support
                         });
                     }
                 }
+
+                IConfigurationSection tagsSection = configurationSection.GetSection("Tags");
+                if (tagsSection.Exists()) {
+                    tags = tagsSection.GetChildren().ToDictionary(s => s.Key, s => s.Value);
+                }
+
+                label = configurationSection["Label"];
+                eTag = configurationSection["ETag"];
+                enableTelemetry = configurationSection.GetValue<bool>("EnableTelemetry");
             }
 
             return new FeatureDefinition()
             {
                 Name = configurationSection.Key,
                 EnabledFor = enabledFor,
-                RequirementType = requirementType
+                RequirementType = requirementType,
+                Label = label,
+                ETag = eTag,
+                EnableTelemetry = enableTelemetry,
+                Tags = tags
             };
         }
 

src/Microsoft.FeatureManagement/FeatureDefinition.cs

@@ -25,5 +25,27 @@ public class FeatureDefinition
         /// The default value is <see cref="RequirementType.Any"/>.
         /// </summary>
         public RequirementType RequirementType { get; set; } = RequirementType.Any;
+
+        /// <summary>
+        /// A value used to group feature flags.
+        /// A <see cref="Label"/> is used together with a <see cref="Name"/> to uniquely identify a feature.
+        /// </summary>
+        public string Label { get; set; }
+
+        /// <summary>
+        /// An ETag indicating the state of a feature. This value is used to determine whether a feature has changed.
+        /// </summary>
+        public string ETag { get; set; }
+
+        /// <summary>
+        /// A dictionary of tags used to assign additional properties to a feature.
+        /// These can be used to indicate how a feature may be applied.
+        /// </summary>
+        public IReadOnlyDictionary<string, string> Tags { get; set; }
+
+        /// <summary>
+        /// A flag to enable or disable sending telemetry events to the registered <see cref="ITelemetryProvider">.
+        /// </summary>
+        public bool EnableTelemetry { get; set; }
     }
 }

src/Microsoft.FeatureManagement/FeatureManager.cs

@@ -5,10 +5,12 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using Microsoft.FeatureManagement.Telemetry;
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace Microsoft.FeatureManagement
@@ -54,6 +56,8 @@ public FeatureManager(
             _parametersCache = new MemoryCache(new MemoryCacheOptions());
         }
 
+        public ITelemetryPublisher TelemetryPublisher { get; init; }
+
         public Task<bool> IsEnabledAsync(string feature)
         {
             return IsEnabledAsync<object>(feature, null, false);
@@ -214,6 +218,24 @@ await contextualFilter.EvaluateAsync(context, appContext).ConfigureAwait(false)
                 await sessionManager.SetAsync(feature, enabled).ConfigureAwait(false);
             }
 
+            if (featureDefinition.EnableTelemetry)
+            {
+                if (TelemetryPublisher == null)
+                {
+                    _logger.LogWarning("The feature declaration enabled telemetry but no telemetry publisher was registered.");
+                } 
+                else
+                {
+                    await TelemetryPublisher.PublishEvent(
+                        new EvaluationEvent
+                        {
+                            FeatureDefinition = featureDefinition,
+                            IsEnabled = enabled
+                        },
+                        CancellationToken.None);
+                }
+            }
+
             return enabled;
         }
 

src/Microsoft.FeatureManagement/IsExternalInit.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+
+// The init accessor for properties is supported in C# 9.0 and later.
+// This class is used to compile .NET frameworks that don't support C# 9.0 or later while still using the init accessor for a property.
+// The code referenced for this file can be found here: https://github.com/dotnet/roslyn/issues/45510#issuecomment-725091019
+
+#if NETSTANDARD2_0 || NETCOREAPP2_1 || NETCOREAPP3_1
+
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    internal static class IsExternalInit
+    {
+    }
+}
+
+#endif

src/Microsoft.FeatureManagement/Microsoft.FeatureManagement.csproj

@@ -15,7 +15,7 @@
     <SignAssembly>true</SignAssembly>
     <DelaySign>false</DelaySign>
     <AssemblyOriginatorKeyFile>..\..\build\Microsoft.FeatureManagement.snk</AssemblyOriginatorKeyFile>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>9.0</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup>

src/Microsoft.FeatureManagement/ServiceCollectionExtensions.cs

@@ -4,7 +4,11 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Microsoft.FeatureManagement.Telemetry;
 using System;
+using System.Collections.Generic;
 
 namespace Microsoft.FeatureManagement
 {
@@ -26,7 +30,16 @@ public static IFeatureManagementBuilder AddFeatureManagement(this IServiceCollec
             // Add required services
             services.TryAddSingleton<IFeatureDefinitionProvider, ConfigurationFeatureDefinitionProvider>();
 
-            services.AddSingleton<IFeatureManager, FeatureManager>();
+            services.TryAddSingleton<IFeatureManager>(sp =>
+                new FeatureManager(
+                    sp.GetRequiredService<IFeatureDefinitionProvider>(),
+                    sp.GetRequiredService<IEnumerable<IFeatureFilterMetadata>>(),
+                    sp.GetRequiredService<IEnumerable<ISessionManager>>(),
+                    sp.GetRequiredService<ILoggerFactory>(),
+                    sp.GetRequiredService<IOptions<FeatureManagementOptions>>())
+                {
+                    TelemetryPublisher = sp.GetService<ITelemetryPublisher>(),
+                });
 
             services.AddSingleton<ISessionManager, EmptySessionManager>();
 

src/Microsoft.FeatureManagement/Telemetry/EvaluationEvent.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+namespace Microsoft.FeatureManagement.Telemetry
+{
+    /// <summary>
+    /// An event representing the evaluation of a feature.
+    /// </summary>
+    public class EvaluationEvent
+    {
+        /// <summary>
+        /// The definition of the feature that was evaluated.
+        /// </summary>
+        public FeatureDefinition FeatureDefinition { get; set; }
+
+        /// <summary>
+        /// The enabled state of the feature after evaluation.
+        /// </summary>
+        public bool IsEnabled { get; set; }
+    }
+}

src/Microsoft.FeatureManagement/Telemetry/ITelemetryPublisher.cs

@@ -0,0 +1,23 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.FeatureManagement.Telemetry
+{
+    /// <summary>
+    /// A publisher of telemetry events.
+    /// </summary>
+    public interface ITelemetryPublisher
+    {
+        /// <summary>
+        /// Handles an EvaluationEvent and publishes it to the configured telemetry channel.
+        /// </summary>
+        /// <param name="evaluationEvent"> The event to publish.</param>
+        /// <param name="cancellationToken"> A cancellation token.</param>
+        /// <returns>ValueTask</returns>
+        public ValueTask PublishEvent(EvaluationEvent evaluationEvent, CancellationToken cancellationToken);
+    }
+
+}