Fix SyncTriggers URI for dedicated linux on app service

Author: ahmelsayed

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

@@ -284,7 +284,13 @@ internal static HttpRequestMessage BuildSetTriggersRequest()
                 protocol = "http";
             }
 
-            var url = $"{protocol}://{Environment.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteHostName)}/operations/settriggers";
+            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 url = $"{protocol}://{hostname}/operations/settriggers";
 
             return new HttpRequestMessage(HttpMethod.Post, url);
         }

test/WebJobs.Script.Tests/Managment/FunctionsSyncManagerTests.cs

@@ -214,6 +214,24 @@ public void Disables_Ssl_If_SkipSslValidation_Enabled(int skipSslValidation, str
             }
         }
 
+        [Theory]
+        [InlineData(EnvironmentSettingNames.AzureWebsiteName, "sitename", "https://sitename.azurewebsites.net/operations/settriggers")]
+        [InlineData(EnvironmentSettingNames.AzureWebsiteHostName, "sitename", "https://sitename/operations/settriggers")]
+        public void Use_Website_Name_If_Website_Hostname_Is_Not_Available(string envKey, string envValue, string expectedSyncTriggersUri)
+        {
+            var vars = new Dictionary<string, string>
+            {
+                { envKey, envValue },
+            };
+
+            using (var env = new TestScopedEnvironmentVariable(vars))
+            {
+                var httpRequest = FunctionsSyncManager.BuildSetTriggersRequest();
+                Assert.Equal(expectedSyncTriggersUri, httpRequest.RequestUri.AbsoluteUri);
+                Assert.Equal(HttpMethod.Post, httpRequest.Method);
+            }
+        }
+
         private static HttpClient CreateHttpClient(MockHttpHandler httpHandler)
         {
             return new HttpClient(httpHandler);