Add failover & load balancing telemetry

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationProvider.cs

@@ -970,7 +970,8 @@ private void SetRequestTracingOptions()
                 IsKeyVaultConfigured = _options.IsKeyVaultConfigured,
                 IsKeyVaultRefreshConfigured = _options.IsKeyVaultRefreshConfigured,
                 ReplicaCount = _options.Endpoints?.Count() - 1 ?? _options.ConnectionStrings?.Count() - 1 ?? 0,
-                FeatureFlagTracing = _options.FeatureFlagTracing
+                FeatureFlagTracing = _options.FeatureFlagTracing,
+                IsLoadBalancingEnabled = _options.LoadBalancingEnabled
             };
         }
 
@@ -1005,6 +1006,11 @@ private async Task<T> ExecuteWithFailOverPolicyAsync<T>(
             Func<ConfigurationClient, Task<T>> funcToExecute,
             CancellationToken cancellationToken = default)
         {
+            if (_requestTracingEnabled && _requestTracingOptions != null)
+            {
+                _requestTracingOptions.IsFailoverRequest = false;
+            }
+
             if (_options.LoadBalancingEnabled && _lastSuccessfulEndpoint != null && clients.Count() > 1)
             {
                 int nextClientIndex = 0;
@@ -1107,6 +1113,11 @@ private async Task<T> ExecuteWithFailOverPolicyAsync<T>(
                 }
 
                 previousEndpoint = currentEndpoint;
+
+                if (_requestTracingEnabled && _requestTracingOptions != null)
+                {
+                    _requestTracingOptions.IsFailoverRequest = true;
+                }
             }
         }
 

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Constants/RequestTracingConstants.cs

@@ -22,20 +22,28 @@ internal class RequestTracingConstants
 
         public const string RequestTypeKey = "RequestType";
         public const string HostTypeKey = "Host";
-        public const string FilterTypeKey = "Filter";
         public const string EnvironmentKey = "Env";
         public const string FeatureManagementVersionKey = "FMVer";
         public const string FeatureManagementAspNetCoreVersionKey = "FMANCVer";
         public const string DevEnvironmentValue = "Dev";
         public const string KeyVaultConfiguredTag = "UsesKeyVault";
         public const string KeyVaultRefreshConfiguredTag = "RefreshesKeyVault";
         public const string ReplicaCountKey = "ReplicaCount";
+        public const string FeaturesKey = "Features";
+        public const string LoadBalancingEnabledTag = "LB";
+        public const string SignalRUsedTag = "SignalR";
+        public const string FailoverRequestTag = "Failover";
+
+        public const string FeatureFlagFilterTypeKey = "Filter";
+        public const string CustomFilter = "CSTM";
+        public const string PercentageFilter = "PRCNT";
+        public const string TimeWindowFilter = "TIME";
+        public const string TargetingFilter = "TRGT";
+        public const string FeatureFlagFeaturesKey = "FFFeatures";
         public const string FeatureFlagUsesTelemetryTag = "Telemetry";
         public const string FeatureFlagUsesSeedTag = "Seed";
         public const string FeatureFlagMaxVariantsKey = "MaxVariants";
         public const string FeatureFlagUsesVariantConfigurationReferenceTag = "ConfigRef";
-        public const string FeatureFlagFeaturesKey = "FFFeatures";
-        public const string SignalRUsedTag = "UsesSignalR";
 
         public const string DiagnosticHeaderActivityName = "Azure.CustomDiagnosticHeaders";
         public const string CorrelationContextHeader = "Correlation-Context";

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/FeatureManagement/FeatureFlagTracing.cs

@@ -14,11 +14,6 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.FeatureManage
     /// </summary>
     internal class FeatureFlagTracing
     {
-        private const string CustomFilter = "CSTM";
-        private const string PercentageFilter = "PRCNT";
-        private const string TimeWindowFilter = "TIME";
-        private const string TargetingFilter = "TRGT";
-
         // Built-in Feature Filter Names
         private readonly List<string> PercentageFilterNames = new List<string> { "Percentage", "Microsoft.Percentage", "PercentageFilter", "Microsoft.PercentageFilter" };
         private readonly List<string> TimeWindowFilterNames = new List<string> { "TimeWindow", "Microsoft.TimeWindow", "TimeWindowFilter", "Microsoft.TimeWindowFilter" };
@@ -98,7 +93,7 @@ public string CreateFiltersString()
 
             if (UsesCustomFilter)
             {
-                sb.Append(CustomFilter);
+                sb.Append(RequestTracingConstants.CustomFilter);
             }
 
             if (UsesPercentageFilter)
@@ -108,7 +103,7 @@ public string CreateFiltersString()
                     sb.Append(RequestTracingConstants.Delimiter);
                 }
 
-                sb.Append(PercentageFilter);
+                sb.Append(RequestTracingConstants.PercentageFilter);
             }
 
             if (UsesTimeWindowFilter)
@@ -118,7 +113,7 @@ public string CreateFiltersString()
                     sb.Append(RequestTracingConstants.Delimiter);
                 }
 
-                sb.Append(TimeWindowFilter);
+                sb.Append(RequestTracingConstants.TimeWindowFilter);
             }
 
             if (UsesTargetingFilter)
@@ -128,14 +123,23 @@ public string CreateFiltersString()
                     sb.Append(RequestTracingConstants.Delimiter);
                 }
 
-                sb.Append(TargetingFilter);
+                sb.Append(RequestTracingConstants.TargetingFilter);
             }
 
             return sb.ToString();
         }
 
+        /// <summary>
+        /// Returns a formatted string containing code names, indicating which tracing features are used by feature flags.
+        /// </summary>
+        /// <returns>Formatted string like: "Seed+ConfigRef+Telemetry". If no tracing features are used, empty string will be returned.</returns>
         public string CreateFeaturesString()
         {
+            if (!UsesAnyTracingFeature())
+            {
+                return string.Empty;
+            }
+
             var sb = new StringBuilder();
 
             if (UsesSeed)

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/RequestTracingOptions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 //
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.FeatureManagement;
+using System.Text;
 
 namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
 {
@@ -51,5 +52,55 @@ internal class RequestTracingOptions
         /// Flag to indicate whether Microsoft.AspNetCore.SignalR assembly is present in the application.
         /// </summary>
         public bool IsSignalRUsed { get; set; } = false;
+
+        /// <summary>
+        /// Flag to indicate whether load balancing is enabled.
+        /// </summary>
+        public bool IsLoadBalancingEnabled { get; set; } = false;
+
+        /// <summary>
+        /// Flag to indicate whether the request is triggered by a failover.
+        /// </summary>
+        public bool IsFailoverRequest { get; set; } = false;
+
+        /// <summary>
+        /// Checks whether any tracing feature is used.
+        /// </summary>
+        /// <returns>True if any tracing feature is used, otherwise false.</returns>
+        public bool UsesAnyTracingFeature()
+        {
+            return IsLoadBalancingEnabled || IsSignalRUsed;
+        }
+
+        /// <summary>
+        /// Returns a formatted string containing code names, indicating which tracing features are used by the application.
+        /// </summary>
+        /// <returns>Formatted string like: "LB+SignalR". If no tracing features are used, empty string will be returned.</returns>
+        public string CreateFeaturesString()
+        {
+            if (!UsesAnyTracingFeature())
+            {
+                return string.Empty;
+            }
+
+            var sb = new StringBuilder();
+
+            if (IsLoadBalancingEnabled)
+            {
+                sb.Append(RequestTracingConstants.LoadBalancingEnabledTag);
+            }
+
+            if (IsSignalRUsed)
+            {
+                if (sb.Length > 0)
+                {
+                    sb.Append(RequestTracingConstants.Delimiter);
+                }
+
+                sb.Append(RequestTracingConstants.SignalRUsedTag);
+            }
+
+            return sb.ToString();
+        }
     }
 }

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/TracingUtils.cs

@@ -158,7 +158,7 @@ private static string CreateCorrelationContextHeader(RequestType requestType, Re
 
             if (requestTracingOptions.FeatureFlagTracing.UsesAnyFeatureFilter())
             {
-                correlationContextKeyValues.Add(new KeyValuePair<string, string>(RequestTracingConstants.FilterTypeKey, requestTracingOptions.FeatureFlagTracing.CreateFiltersString()));
+                correlationContextKeyValues.Add(new KeyValuePair<string, string>(RequestTracingConstants.FeatureFlagFilterTypeKey, requestTracingOptions.FeatureFlagTracing.CreateFiltersString()));
             }
 
             if (requestTracingOptions.FeatureFlagTracing.MaxVariants > 0)
@@ -181,6 +181,11 @@ private static string CreateCorrelationContextHeader(RequestType requestType, Re
                 correlationContextKeyValues.Add(new KeyValuePair<string, string>(RequestTracingConstants.FeatureManagementAspNetCoreVersionKey, requestTracingOptions.FeatureManagementAspNetCoreVersion));
             }
 
+            if (requestTracingOptions.UsesAnyTracingFeature())
+            {
+                correlationContextKeyValues.Add(new KeyValuePair<string, string>(RequestTracingConstants.FeaturesKey, requestTracingOptions.CreateFeaturesString()));
+            }
+
             if (requestTracingOptions.IsKeyVaultConfigured)
             {
                 correlationContextTags.Add(RequestTracingConstants.KeyVaultConfiguredTag);
@@ -191,9 +196,9 @@ private static string CreateCorrelationContextHeader(RequestType requestType, Re
                 correlationContextTags.Add(RequestTracingConstants.KeyVaultRefreshConfiguredTag);
             }
 
-            if (requestTracingOptions.IsSignalRUsed)
+            if (requestTracingOptions.IsFailoverRequest)
             {
-                correlationContextTags.Add(RequestTracingConstants.SignalRUsedTag);
+                correlationContextTags.Add(RequestTracingConstants.FailoverRequestTag);
             }
 
             var sb = new StringBuilder();