Do not start languageworkers when using pooling (#4895)

Author: pragnagopa

src/WebJobs.Script/Environment/EnvironmentExtensions.cs

@@ -48,6 +48,12 @@ public static bool IsPlaceholderModeEnabled(this IEnvironment environment)
             return environment.GetEnvironmentVariable(AzureWebsitePlaceholderMode) == "1";
         }
 
+        public static bool IsLegacyPlaceholderTemplateSite(this IEnvironment environment)
+        {
+            string siteName = environment.GetEnvironmentVariable(AzureWebsiteName);
+            return string.IsNullOrEmpty(siteName) ? false : siteName.Equals(ScriptConstants.LegacyPlaceholderTemplateSiteName, StringComparison.InvariantCultureIgnoreCase);
+        }
+
         public static bool IsEasyAuthEnabled(this IEnvironment environment)
         {
             bool.TryParse(environment.GetEnvironmentVariable(EnvironmentSettingNames.EasyAuthEnabled), out bool isEasyAuthEnabled);

src/WebJobs.Script/Rpc/RpcInitializationService.cs

@@ -150,9 +150,18 @@ private Task InitializeWebHostRuntimeChannelsAsync()
             return Task.CompletedTask;
         }
 
-        private bool ShouldStartInPlaceholderMode()
+        internal bool ShouldStartInPlaceholderMode()
         {
-            return string.IsNullOrEmpty(_workerRuntime) && _environment.IsPlaceholderModeEnabled();
+            if (string.IsNullOrEmpty(_workerRuntime) && _environment.IsPlaceholderModeEnabled())
+            {
+                if (_environment.IsLinuxHostingEnvironment())
+                {
+                    return true;
+                }
+                // On Windows AppService Env, only start worker processes for legacy template site: FunctionsPlaceholderTemplateSite
+                return _environment.IsLegacyPlaceholderTemplateSite();
+            }
+            return false;
         }
 
         // To help with unit tests

src/WebJobs.Script/ScriptConstants.cs

@@ -22,6 +22,8 @@ public static class ScriptConstants
         public const string JobHostMiddlewarePipelineRequestDelegate = "MS_JobHostMiddlewarePipelineRequestDelegate";
         public const string HstsMiddlewareRequestDelegate = "MS_HstsMiddlewareRequestDelegate";
 
+        public const string LegacyPlaceholderTemplateSiteName = "FunctionsPlaceholderTemplateSite";
+
         public const string LogPropertyPrimaryHostKey = "MS_PrimaryHost";
         public const string LogPropertySourceKey = "MS_Source";
         public const string LogPropertyFunctionNameKey = "MS_FunctionName";

test/WebJobs.Script.Tests/Rpc/RpcInitializationServiceTests.cs

@@ -67,6 +67,7 @@ public async Task RpcInitializationService_Initializes_RpcServerAndChannels_Wind
             var mockEnvironment = new Mock<IEnvironment>();
             mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsitePlaceholderMode)).Returns("1");
             mockEnvironment.Setup(p => p.GetEnvironmentVariable(LanguageWorkerConstants.FunctionWorkerRuntimeSettingName)).Returns(string.Empty);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteName)).Returns("functionsPlaceholderTemplateSite");
 
             _rpcInitializationService = new RpcInitializationService(_optionsMonitor, mockEnvironment.Object, testRpcServer, _mockLanguageWorkerChannelManager.Object, _logger);
             await _rpcInitializationService.StartAsync(CancellationToken.None);
@@ -287,5 +288,21 @@ public async Task RpcInitializationService_TriggerShutdown_KillGetsCalledWhenShu
             testRpcServer.Verify(a => a.ShutdownAsync(), Times.Once);
             testRpcServer.Verify(a => a.KillAsync(), Times.Once);
         }
+
+        [Theory]
+        [InlineData("1", "functionsPlaceholderTemplateSite", "1234", true)]
+        [InlineData("0", "functionsPlaceholderTemplateSite", "1234", false)]
+        [InlineData("1", "functionsPlaceholderTemplateSitejava", "1234", false)]
+        [InlineData("1", "functionsPlaceholderTemplateSite", "", true)]
+        public void ShouldStartInPlaceholderMode_Returns_ExpectedValue(string placeholderMode, string siteName, string siteInstanaceId, bool expectedResult)
+        {
+            Mock<IRpcServer> testRpcServer = new Mock<IRpcServer>();
+            var mockEnvironment = new Mock<IEnvironment>();
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsitePlaceholderMode)).Returns(placeholderMode);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteName)).Returns(siteName);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteInstanceId)).Returns(siteInstanaceId);
+            _rpcInitializationService = new RpcInitializationService(_optionsMonitor, mockEnvironment.Object, testRpcServer.Object, _mockLanguageWorkerChannelManager.Object, _logger);
+            Assert.Equal(_rpcInitializationService.ShouldStartInPlaceholderMode(), expectedResult);
+        }
     }
 }