Fix Linux Consumption PlaceholderMode initialization (#4015)

Author: mathewc

src/WebJobs.Script.WebHost/Program.cs

@@ -19,14 +19,9 @@ public class Program
     {
         public static void Main(string[] args)
         {
-            var host = BuildWebHost(args);
+            InitializeProcess();
 
-            var environment = host.Services.GetService<IEnvironment>();
-            if (environment.IsLinuxContainerEnvironment())
-            {
-                // Linux containers always start out in placeholder mode
-                environment.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebsitePlaceholderMode, "1");
-            }
+            var host = BuildWebHost(args);
 
             host.RunAsync()
                 .Wait();
@@ -76,5 +71,18 @@ public static IWebHostBuilder CreateWebHostBuilder(string[] args = null)
                 })
                 .UseStartup<Startup>();
         }
+
+        /// <summary>
+        /// Perform any process level initialization that needs to happen BEFORE
+        /// the WebHost is initialized.
+        /// </summary>
+        private static void InitializeProcess()
+        {
+            if (SystemEnvironment.Instance.IsLinuxContainerEnvironment())
+            {
+                // Linux containers always start out in placeholder mode
+                SystemEnvironment.Instance.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebsitePlaceholderMode, "1");
+            }
+        }
     }
 }

src/WebJobs.Script.WebHost/Standby/StandbyManager.cs

@@ -109,23 +109,7 @@ public async Task InitializeAsync()
             {
                 try
                 {
-                    string scriptPath = _options.CurrentValue.ScriptPath;
-                    _logger.LogInformation($"Creating StandbyMode placeholder function directory ({scriptPath})");
-
-                    await FileUtility.DeleteDirectoryAsync(scriptPath, true);
-                    FileUtility.EnsureDirectoryExists(scriptPath);
-
-                    string content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.host.json");
-                    File.WriteAllText(Path.Combine(scriptPath, "host.json"), content);
-
-                    string functionPath = Path.Combine(scriptPath, WarmUpConstants.FunctionName);
-                    Directory.CreateDirectory(functionPath);
-                    content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.{WarmUpConstants.FunctionName}.function.json");
-                    File.WriteAllText(Path.Combine(functionPath, "function.json"), content);
-                    content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.{WarmUpConstants.FunctionName}.run.csx");
-                    File.WriteAllText(Path.Combine(functionPath, "run.csx"), content);
-
-                    _logger.LogInformation($"StandbyMode placeholder function directory created");
+                    await CreateStandbyWarmupFunctions();
 
                     // start a background timer to identify when specialization happens
                     // specialization usually happens via an http request (e.g. scale controller
@@ -140,6 +124,27 @@ public async Task InitializeAsync()
             }
         }
 
+        private async Task CreateStandbyWarmupFunctions()
+        {
+            string scriptPath = _options.CurrentValue.ScriptPath;
+            _logger.LogInformation($"Creating StandbyMode placeholder function directory ({scriptPath})");
+
+            await FileUtility.DeleteDirectoryAsync(scriptPath, true);
+            FileUtility.EnsureDirectoryExists(scriptPath);
+
+            string content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.host.json");
+            File.WriteAllText(Path.Combine(scriptPath, "host.json"), content);
+
+            string functionPath = Path.Combine(scriptPath, WarmUpConstants.FunctionName);
+            Directory.CreateDirectory(functionPath);
+            content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.{WarmUpConstants.FunctionName}.function.json");
+            File.WriteAllText(Path.Combine(functionPath, "function.json"), content);
+            content = FileUtility.ReadResourceString($"{ScriptConstants.ResourcePath}.Functions.{WarmUpConstants.FunctionName}.run.csx");
+            File.WriteAllText(Path.Combine(functionPath, "run.csx"), content);
+
+            _logger.LogInformation($"StandbyMode placeholder function directory created");
+        }
+
         private void OnSpecializationTimerTick(object state)
         {
             if (!_webHostEnvironment.InStandbyMode && _environment.IsContainerReady())