Log application start up errors (#5933)

Author: pragnagopa

src/WebJobs.Script.WebHost/Global.asax.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Linq;
 using System.Net;
 using System.Threading;
@@ -74,7 +75,25 @@ internal static string GetShadowCopyPath(string currentShadowCopyDirectories, st
 
         protected void Application_Error(object sender, EventArgs e)
         {
-            // TODO: Log any unhandled exceptions
+            EventGenerator eventGenerator = new EventGenerator();
+
+            // Get the exception object.
+            Exception exc = Server.GetLastError();
+            string subscriptionId = Utility.GetSubscriptionId() ?? string.Empty;
+            string appName = Utility.GetWebsiteUniqueSlotName() ?? string.Empty;
+            eventGenerator.LogFunctionTraceEvent(TraceLevel.Error,
+                                                subscriptionId,
+                                                appName,
+                                                string.Empty,
+                                                string.Empty,
+                                                "Host.Startup",
+                                                exc.StackTrace,
+                                                "Application start up failed.",
+                                                exc.GetType().ToString(),
+                                                exc.Message,
+                                                string.Empty,
+                                                string.Empty,
+                                                string.Empty);
         }
 
         protected void Application_End(object sender, EventArgs e)

src/WebJobs.Script/Config/ScriptSettingsManager.cs

@@ -45,16 +45,7 @@ public virtual string AzureWebsiteUniqueSlotName
         {
             get
             {
-                string name = GetSetting(EnvironmentSettingNames.AzureWebsiteName);
-                string slotName = GetSetting(EnvironmentSettingNames.AzureWebsiteSlotName);
-
-                if (!string.IsNullOrEmpty(slotName) &&
-                    !string.Equals(slotName, ScriptConstants.DefaultProductionSlotName, StringComparison.OrdinalIgnoreCase))
-                {
-                    name += $"-{slotName}";
-                }
-
-                return name?.ToLowerInvariant();
+                return Utility.GetWebsiteUniqueSlotName();
             }
         }
 
@@ -77,12 +68,7 @@ public virtual string ApplicationInsightsInstrumentationKey
 
         public virtual string GetSetting(string settingKey)
         {
-            if (string.IsNullOrEmpty(settingKey))
-            {
-                throw new ArgumentNullException(nameof(settingKey));
-            }
-
-            return Environment.GetEnvironmentVariable(settingKey);
+            return Utility.GetSetting(settingKey);
         }
 
         public string GetSettingOrDefault(string settingKey, string defaultValue)

src/WebJobs.Script/Utility.cs

@@ -180,6 +180,30 @@ public static string GetSubscriptionId()
             return null;
         }
 
+        public static string GetWebsiteUniqueSlotName()
+        {
+            string name = GetSetting(EnvironmentSettingNames.AzureWebsiteName);
+            string slotName = GetSetting(EnvironmentSettingNames.AzureWebsiteSlotName);
+
+            if (!string.IsNullOrEmpty(slotName) &&
+                !string.Equals(slotName, ScriptConstants.DefaultProductionSlotName, StringComparison.OrdinalIgnoreCase))
+            {
+                name += $"-{slotName}";
+            }
+
+            return name?.ToLowerInvariant();
+        }
+
+        public static string GetSetting(string settingKey)
+        {
+            if (string.IsNullOrEmpty(settingKey))
+            {
+                throw new ArgumentNullException(nameof(settingKey));
+            }
+
+            return Environment.GetEnvironmentVariable(settingKey);
+        }
+
         public static bool IsValidUserType(Type type)
         {
             return !type.IsInterface && !type.IsPrimitive && !(type.Namespace == "System");