[Azure Monitor Exporter] Add custom resource support (#53432)

* Add custom resource.

* changelog update

Author: rajkumar-rangaraj

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ### Features Added
 
+* Enabled resource metrics export by default.
+  ([#53432](https://github.com/Azure/azure-sdk-for-net/pull/53432))
+
 ### Breaking Changes
 
 ### Bugs Fixed

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Internals/ResourceExtensions.cs

@@ -138,7 +138,7 @@ internal static class ResourceExtensions
         try
         {
             var exportResource = platform.GetEnvironmentVariable(EnvironmentVariableConstants.EXPORT_RESOURCE_METRIC);
-            if (exportResource != null && exportResource.Equals("true", StringComparison.OrdinalIgnoreCase))
+            if (exportResource == null || exportResource.Equals("true", StringComparison.OrdinalIgnoreCase))
             {
                 shouldReportMetricTelemetry = true;
             }

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/tests/Azure.Monitor.OpenTelemetry.Exporter.Tests/ResourceExtensionsTests.cs

@@ -49,7 +49,7 @@ public void DefaultResource(string? instrumentationKey, string envVarValue)
 
         Assert.StartsWith("unknown_service", azMonResource?.RoleName);
         Assert.Equal(Dns.GetHostName(), azMonResource?.RoleInstance);
-        if (envVarValue == "true")
+        if (envVarValue == "true" || envVarValue == null)
         {
             Assert.Equal(instrumentationKey != null, azMonResource?.MonitorBaseData != null);
         }
@@ -338,7 +338,7 @@ public void MetricTelemetryIsAddedToResourceBasedOnEnvVar(string envVarValue)
         var resource = ResourceBuilder.CreateDefault().Build();
         var azMonResource = resource.CreateAzureMonitorResource(platform: GetMockPlatform(enableResourceMetric: envVarValue), instrumentationKey: InstrumentationKey);
 
-        if (envVarValue == "true")
+        if (envVarValue == "true" || envVarValue == null)
         {
             Assert.NotNull(azMonResource?.MonitorBaseData);
         }

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/tests/Azure.Monitor.OpenTelemetry.Exporter.Tests/StandardMetricTests.cs

@@ -507,7 +507,21 @@ public void ValidatePerfCounterMetrics()
             tracerProvider?.ForceFlush();
             WaitForActivityExport(traceTelemetryItems);
 
-            standardMetricCustomProcessor._meterProvider?.ForceFlush();
+            // Wait for performance counter collection cycle to complete
+            // Performance counters are collected periodically, so we need to wait for at least one collection cycle
+            var perfCountersCollected = SpinWait.SpinUntil(
+                condition: () =>
+                {
+                    standardMetricCustomProcessor._meterProvider?.ForceFlush();
+                    Thread.Sleep(100);
+                    var requestRate = metricTelemetryItems
+                        .Select(ti => (MetricsData)ti.Data.BaseData)
+                        .FirstOrDefault(md => md.Metrics.Count > 0 && md.Metrics[0].Name == PerfCounterConstants.RequestRateMetricIdValue);
+                    return requestRate != null && requestRate.Metrics[0].Value >= 1;
+                },
+                timeout: TimeSpan.FromSeconds(5));
+
+            Assert.True(perfCountersCollected, "Performance counter metrics were not collected within the timeout period.");
 
             // We expect multiple metric telemetry items now (at least one per perf counter plus request duration histogram).
             Assert.True(metricTelemetryItems.Count >= 2, "Expected multiple metric telemetry items including perf counters.");