[AzureMonitorExporter] emit warning if LiveMetrics not supported (Azure#49830)

* minor change, emit warning if LiveMetrics not supported

* Revert "minor change, emit warning if LiveMetrics not supported"

This reverts commit 91313c9.

* pr feedback

* cleanup

* cleanup

* rephrase warning message

Author: Timothy Mothra

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/AzureMonitorExporterExtensions.cs

@@ -7,6 +7,7 @@
 using System.Diagnostics;
 using Azure.Core;
 using Azure.Monitor.OpenTelemetry.Exporter.Internals;
+using Azure.Monitor.OpenTelemetry.Exporter.Internals.Diagnostics;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
 using OpenTelemetry;
@@ -73,6 +74,11 @@ public static TracerProviderBuilder AddAzureMonitorTraceExporter(
                     configure(exporterOptions);
                 }
 
+                if (exporterOptions.EnableLiveMetrics == true)
+                {
+                    AzureMonitorExporterEventSource.Log.LiveMetricsNotSupported(methodName: nameof(AddAzureMonitorTraceExporter));
+                }
+
                 builder.SetSampler(new ApplicationInsightsSampler(exporterOptions.SamplingRatio));
 
                 if (credential != null)
@@ -138,6 +144,11 @@ public static MeterProviderBuilder AddAzureMonitorMetricExporter(
                     configure(exporterOptions);
                 }
 
+                if (exporterOptions.EnableLiveMetrics == true)
+                {
+                    AzureMonitorExporterEventSource.Log.LiveMetricsNotSupported(methodName: nameof(AddAzureMonitorMetricExporter));
+                }
+
                 if (credential != null)
                 {
                     // Credential can be set by either AzureMonitorExporterOptions or Extension Method Parameter.
@@ -176,6 +187,11 @@ public static OpenTelemetryLoggerOptions AddAzureMonitorLogExporter(
             var options = new AzureMonitorExporterOptions();
             configure?.Invoke(options);
 
+            if (options.EnableLiveMetrics == true)
+            {
+                AzureMonitorExporterEventSource.Log.LiveMetricsNotSupported(methodName: nameof(AddAzureMonitorLogExporter));
+            }
+
             if (credential != null)
             {
                 // Credential can be set by either AzureMonitorExporterOptions or Extension Method Parameter.
@@ -236,6 +252,11 @@ public static LoggerProviderBuilder AddAzureMonitorLogExporter(
                     exporterOptions = sp.GetRequiredService<IOptionsMonitor<AzureMonitorExporterOptions>>().Get(finalOptionsName);
                 }
 
+                if (exporterOptions.EnableLiveMetrics == true)
+                {
+                    AzureMonitorExporterEventSource.Log.LiveMetricsNotSupported(methodName: nameof(AddAzureMonitorLogExporter));
+                }
+
                 if (credential != null)
                 {
                     // Credential can be set by either AzureMonitorExporterOptions or Extension Method Parameter.

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/AzureMonitorExporterOptions.cs

@@ -91,10 +91,12 @@ public enum ServiceVersion
         /// Note: Enabling Live Metrics incurs no additional billing or costs. However, it does introduce
         /// a performance overhead due to extra data collection, processing, and networking calls. This overhead
         /// is only significant when the LiveMetrics portal is actively used in the UI. Once the portal is closed,
+        /// </summary>
         /// LiveMetrics reverts to a 'silent' mode with minimal to no overhead.
+        /// <remarks>
         /// This setting is applicable only when `UseAzureMonitorExporter` API is used.
         /// <see href="https://learn.microsoft.com/azure/azure-monitor/app/live-stream"/>.
-        /// </summary>
+        /// </remarks>
         public bool EnableLiveMetrics { get; set; } = true;
 
         /// <summary>

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Internals/Diagnostics/AzureMonitorExporterEventSource.cs

@@ -455,5 +455,8 @@ public void ConfigureFailed(System.Exception ex)
 
         [Event(44, Message = "Failed to configure AzureMonitorExporterOptions using the connection string from environment variables due to an exception: {0}", Level = EventLevel.Error)]
         public void ConfigureFailed(string exceptionMessage) => WriteEvent(44, exceptionMessage);
+
+        [Event(45, Message = "The {0} method received an AzureMonitorExporterOptions with EnableLiveMetrics set to true, which isn't supported. Note that LiveMetrics is only available via the UseAzureMonitorExporter API.", Level = EventLevel.Warning)]
+        public void LiveMetricsNotSupported(string methodName) => WriteEvent(45, methodName);
     }
 }