[AzureMonitorExporter] Refactor Environment Variables (Azure#38012)

* refactor Env Vars

* cleanup

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

@@ -62,7 +62,7 @@ internal static ConnectionVars InitializeConnectionVars(AzureMonitorExporterOpti
         {
             if (options.ConnectionString == null)
             {
-                var connectionString = platform.GetEnvironmentVariable("APPLICATIONINSIGHTS_CONNECTION_STRING");
+                var connectionString = platform.GetEnvironmentVariable(EnvironmentVariableConstants.APPLICATIONINSIGHTS_CONNECTION_STRING);
 
                 if (!string.IsNullOrWhiteSpace(connectionString))
                 {
@@ -137,7 +137,7 @@ private static ApplicationInsightsRestClient InitializeRestClient(AzureMonitorEx
             {
                 try
                 {
-                    var disableStatsbeat = platform.GetEnvironmentVariable("APPLICATIONINSIGHTS_STATSBEAT_DISABLED");
+                    var disableStatsbeat = platform.GetEnvironmentVariable(EnvironmentVariableConstants.APPLICATIONINSIGHTS_STATSBEAT_DISABLED);
                     if (string.Equals(disableStatsbeat, "true", StringComparison.OrdinalIgnoreCase))
                     {
                         AzureMonitorExporterEventSource.Log.StatsbeatDisabled();

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

@@ -0,0 +1,59 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+namespace Azure.Monitor.OpenTelemetry.Exporter.Internals
+{
+    internal static class EnvironmentVariableConstants
+    {
+        /// <summary>
+        /// Available for users to set their Connection String.
+        /// </summary>
+        /// <remarks>
+        /// <see href="https://learn.microsoft.com/azure/azure-monitor/app/opentelemetry-configuration?#connection-string"/>.
+        /// </remarks>
+        public const string APPLICATIONINSIGHTS_CONNECTION_STRING = "APPLICATIONINSIGHTS_CONNECTION_STRING";
+
+        /// <summary>
+        /// Available for users to opt-out of Statsbeat.
+        /// </summary>
+        /// <remarks>
+        /// <see href="https://learn.microsoft.com/azure/azure-monitor/app/statsbeat"/>.
+        /// </remarks>
+        public const string APPLICATIONINSIGHTS_STATSBEAT_DISABLED = "APPLICATIONINSIGHTS_STATSBEAT_DISABLED";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by Statsbeat to identify if the Exporter is running within Azure Functions.
+        /// </summary>
+        public const string FUNCTIONS_WORKER_RUNTIME = "FUNCTIONS_WORKER_RUNTIME";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by PersistentStorage to identify a Windows temp directory to save telemetry.
+        /// </summary>
+        public const string LOCALAPPDATA = "LOCALAPPDATA";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by PersistentStorage to identify a Windows temp directory to save telemetry.
+        /// </summary>
+        public const string TEMP = "TEMP";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by PersistentStorage to identify a Linux temp directory to save telemetry.
+        /// </summary>
+        public const string TMPDIR = "TMPDIR";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by Statsbeat to get the App Service Host Name.
+        /// </summary>
+        public const string WEBSITE_HOME_STAMPNAME = "WEBSITE_HOME_STAMPNAME";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by Statsbeat to identify Azure Functions.
+        /// </summary>
+        public const string WEBSITE_HOSTNAME = "WEBSITE_HOSTNAME";
+
+        /// <summary>
+        /// INTERNAL ONLY. Used by Statsbeat to get the App Service Website Name.
+        /// </summary>
+        public const string WEBSITE_SITE_NAME = "WEBSITE_SITE_NAME";
+    }
+}

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Internals/PersistentStorage/StorageHelper.cs

@@ -34,15 +34,15 @@ internal static string GetStorageDirectory(IPlatform platform, string? configure
 
             if (platform.IsOSPlatform(OSPlatform.Windows))
             {
-                if (TryCreateTelemetryDirectory(platform: platform, path: environmentVars["LOCALAPPDATA"]?.ToString(), createdDirectoryPath: out dirPath)
-                    || TryCreateTelemetryDirectory(platform: platform, path: environmentVars["TEMP"]?.ToString(), createdDirectoryPath: out dirPath))
+                if (TryCreateTelemetryDirectory(platform: platform, path: environmentVars[EnvironmentVariableConstants.LOCALAPPDATA]?.ToString(), createdDirectoryPath: out dirPath)
+                    || TryCreateTelemetryDirectory(platform: platform, path: environmentVars[EnvironmentVariableConstants.TEMP]?.ToString(), createdDirectoryPath: out dirPath))
                 {
                     return dirPath;
                 }
             }
             else
             {
-                if (TryCreateTelemetryDirectory(platform: platform, path: environmentVars["TMPDIR"]?.ToString(), createdDirectoryPath: out dirPath)
+                if (TryCreateTelemetryDirectory(platform: platform, path: environmentVars[EnvironmentVariableConstants.TMPDIR]?.ToString(), createdDirectoryPath: out dirPath)
                     || TryCreateTelemetryDirectory(platform: platform, path: "/var/tmp/", createdDirectoryPath: out dirPath)
                     || TryCreateTelemetryDirectory(platform: platform, path: "/tmp/", createdDirectoryPath: out dirPath))
                 {

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/Internals/Statsbeat/AzureMonitorStatsbeat.cs

@@ -144,12 +144,12 @@ private Measurement<int> GetAttachStatsbeat()
 
         private void SetResourceProviderDetails(IPlatform platform)
         {
-            var appSvcWebsiteName = platform.GetEnvironmentVariable("WEBSITE_SITE_NAME");
+            var appSvcWebsiteName = platform.GetEnvironmentVariable(EnvironmentVariableConstants.WEBSITE_SITE_NAME);
             if (appSvcWebsiteName != null)
             {
                 _resourceProvider = "appsvc";
                 _resourceProviderId = appSvcWebsiteName;
-                var appSvcWebsiteHostName = platform.GetEnvironmentVariable("WEBSITE_HOME_STAMPNAME");
+                var appSvcWebsiteHostName = platform.GetEnvironmentVariable(EnvironmentVariableConstants.WEBSITE_HOME_STAMPNAME);
                 if (!string.IsNullOrEmpty(appSvcWebsiteHostName))
                 {
                     _resourceProviderId += "/" + appSvcWebsiteHostName;
@@ -158,11 +158,11 @@ private void SetResourceProviderDetails(IPlatform platform)
                 return;
             }
 
-            var functionsWorkerRuntime = platform.GetEnvironmentVariable("FUNCTIONS_WORKER_RUNTIME");
+            var functionsWorkerRuntime = platform.GetEnvironmentVariable(EnvironmentVariableConstants.FUNCTIONS_WORKER_RUNTIME);
             if (functionsWorkerRuntime != null)
             {
                 _resourceProvider = "functions";
-                _resourceProviderId = platform.GetEnvironmentVariable("WEBSITE_HOSTNAME");
+                _resourceProviderId = platform.GetEnvironmentVariable(EnvironmentVariableConstants.WEBSITE_HOSTNAME);
 
                 return;
             }