Fixing WEBSITE_HOSTNAME issue (#4162)

Author: mathewc

src/WebJobs.Script.WebHost/App_Start/WebHostResolver.cs

@@ -153,6 +153,9 @@ internal void EnsureInitialized(WebHostSettings settings)
                             // settings configured by the user (WEBSITE_TIME_ZONE) are honored.
                             // DateTime caches timezone information, so we need to clear the cache.
                             TimeZoneInfo.ClearCachedData();
+
+                            // ensure we reinitialize hostname after specialization
+                            HostNameProvider.Reset();
                         }
 
                         if (_standbyHostManager != null)

src/WebJobs.Script.WebHost/Extensions/FunctionMetadataExtensions.cs

@@ -170,8 +170,8 @@ internal static string GetScmBaseUrl()
         {
             // VFS APIs aren't exposed by the v1 runtime, so we must redirect
             // to the SCM site
-            string hostName = Environment.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteHostName);
-            
+            string hostName = HostNameProvider.Value;
+
             string scmHostName = null;
             if (!string.IsNullOrEmpty(hostName))
             {
@@ -195,7 +195,7 @@ internal static string GetScmBaseUrl()
 
         internal static string GetAppBaseUrl()
         {
-            string hostName = Environment.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteHostName) ?? "localhost";
+            string hostName = HostNameProvider.Value ?? "localhost";
             return $"https://{hostName}";
         }
 

src/WebJobs.Script.WebHost/Handlers/SystemTraceHandler.cs

@@ -29,6 +29,8 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
                     .WithDefaults(ScriptConstants.TraceSourceHttpHandler);
 
             SetRequestId(request);
+            HostNameProvider.Synchronize(request, traceWriter);
+
             if (request.IsColdStart())
             {
                 // for cold start requests we want to measure the request

src/WebJobs.Script.WebHost/HostNameProvider.cs

@@ -0,0 +1,66 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using Microsoft.Azure.WebJobs.Host;
+using Microsoft.Azure.WebJobs.Script.Config;
+
+namespace Microsoft.Azure.WebJobs.Script.WebHost
+{
+    /// <summary>
+    /// Provides the current HostName for the Function App.
+    /// <remarks>
+    /// The environment value for WEBSITE_HOSTNAME is unreliable and shouldn't be used directly. AppService site swaps change
+    /// the site’s hostname under the covers, and the worker process is NOT recycled (for performance reasons). That means the
+    /// site will continue to run with the same hostname environment variable, leading to an incorrect host name.
+    ///
+    /// WAS_DEFAULT_HOSTNAME is a header injected by front end on every request which provides the correct hostname. We check
+    /// this header on all http requests, and updated the cached hostname value as needed.
+    /// </remarks>
+    /// </summary>
+    public static class HostNameProvider
+    {
+        private static string _hostName;
+
+        public static string Value
+        {
+            get
+            {
+                if (string.IsNullOrEmpty(_hostName))
+                {
+                    // default to the the value specified in environment
+                    var settings = ScriptSettingsManager.Instance;
+                    _hostName = settings.GetSetting(EnvironmentSettingNames.AzureWebsiteHostName);
+                    if (string.IsNullOrEmpty(_hostName))
+                    {
+                        string websiteName = settings.GetSetting(EnvironmentSettingNames.AzureWebsiteName);
+                        if (!string.IsNullOrEmpty(websiteName))
+                        {
+                            _hostName = $"{websiteName}.azurewebsites.net";
+                        }
+                    }
+                }
+                return _hostName;
+            }
+        }
+
+        public static void Synchronize(HttpRequestMessage request, TraceWriter traceWriter)
+        {
+            string hostNameHeaderValue = request.GetHeaderValueOrDefault(ScriptConstants.AntaresDefaultHostNameHeader);
+            if (!string.IsNullOrEmpty(hostNameHeaderValue) &&
+                string.Compare(Value, hostNameHeaderValue) != 0)
+            {
+                traceWriter.InfoFormat("HostName updated from '{0}' to '{1}'", Value, hostNameHeaderValue);
+                _hostName = hostNameHeaderValue;
+            }
+        }
+
+        internal static void Reset()
+        {
+            _hostName = null;
+        }
+    }
+}

src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs

@@ -387,18 +387,13 @@ private async Task<Dictionary<string, string>> ReadDurableTaskConfig()
         internal static HttpRequestMessage BuildSetTriggersRequest()
         {
             var protocol = "https";
-            // On private stamps with no ssl certificate use http instead.
             if (Environment.GetEnvironmentVariable(EnvironmentSettingNames.SkipSslValidation) == "1")
             {
+                // On private stamps with no ssl certificate use http instead.
                 protocol = "http";
             }
 
-            var hostname = Environment.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteHostName);
-            // Linux Dedicated on AppService doesn't have WEBSITE_HOSTNAME
-            hostname = string.IsNullOrWhiteSpace(hostname)
-                ? $"{Environment.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteName)}.azurewebsites.net"
-                : hostname;
-
+            var hostname = HostNameProvider.Value;
             var url = $"{protocol}://{hostname}/operations/settriggers";
 
             return new HttpRequestMessage(HttpMethod.Post, url);

src/WebJobs.Script.WebHost/Security/ScriptSecrets.cs

@@ -17,7 +17,6 @@ public abstract class ScriptSecrets
     {
         protected ScriptSecrets()
         {
-            HostName = ScriptSettingsManager.Instance.GetSetting(EnvironmentSettingNames.AzureWebsiteHostName);
             InstanceId = ScriptSettingsManager.Instance.InstanceId;
             Source = ScriptConstants.Runtime;
         }

src/WebJobs.Script.WebHost/Security/SecretManager.cs

@@ -47,8 +47,7 @@ public SecretManager(ISecretsRepository repository, IKeyValueConverterFactory ke
 
             if (createHostSecretsIfMissing)
             {
-                // The SecretManager implementation of GetHostSecrets will
-                // create a host secret if one is not present.
+                // GetHostSecrets will create host secrets if not present
                 GetHostSecretsAsync().GetAwaiter().GetResult();
             }
 
@@ -461,6 +460,11 @@ private Task RefreshSecretsAsync<T>(T secrets, string keyScope = null) where T :
 
         private async Task PersistSecretsAsync<T>(T secrets, string keyScope = null, bool isNonDecryptable = false) where T : ScriptSecrets
         {
+            if (secrets != null)
+            {
+                secrets.HostName = HostNameProvider.Value;
+            }
+
             ScriptSecretsType secretsType = secrets.SecretsType;
             string secretsContent = ScriptSecretSerializer.SerializeSecrets<T>(secrets);
             if (isNonDecryptable)

src/WebJobs.Script.WebHost/Swagger/SwaggerDocumentManager.cs

@@ -36,7 +36,7 @@ public SwaggerDocumentManager(ScriptHostConfiguration hostConfig)
         public JObject GenerateSwaggerDocument(HttpRouteCollection routes)
         {
             var swaggerDocument = new SwaggerDocument();
-            string hostname = ScriptSettingsManager.Instance.GetSetting(EnvironmentSettingNames.AzureWebsiteHostName);
+            string hostname = HostNameProvider.Value;
             swaggerDocument.SwaggerInfo.FunctionAppName = hostname;
             swaggerDocument.Host = hostname;
             swaggerDocument.ApiEndpoints = GetEndpointsData(routes);

src/WebJobs.Script.WebHost/WebHooks/WebJobsSdkExtensionHookProvider.cs

@@ -52,8 +52,7 @@ public Uri GetUrl(IExtensionConfigProvider extension)
         // Provides the URL for accessing the admin extensions WebHook route.
         private Uri GetExtensionWebHookRoute(string extensionName)
         {
-            var settings = ScriptSettingsManager.Instance;
-            var hostName = settings.GetSetting(EnvironmentSettingNames.AzureWebsiteHostName);
+            var hostName = HostNameProvider.Value;
             if (hostName == null)
             {
                 return null;

src/WebJobs.Script.WebHost/WebJobs.Script.WebHost.csproj

@@ -510,6 +510,7 @@
     <Compile Include="Extensions\IEnumerableTasksExtensions.cs" />
     <Compile Include="Filters\EnableDebugModeAttribute.cs" />
     <Compile Include="Filters\RequiresRunningHostAttribute.cs" />
+    <Compile Include="HostNameProvider.cs" />
     <Compile Include="Management\FunctionsSyncManager.cs" />
     <Compile Include="Management\IFunctionsSyncManager.cs" />
     <Compile Include="Management\IWebFunctionsManager.cs" />