Emit diagnostic warning for deprecated Azure Functions Proxies usage

src/WebJobs.Script/Diagnostics/DiagnosticEventConstants.cs

@@ -34,5 +34,8 @@ internal static class DiagnosticEventConstants
 
         public const string WorkerRuntimeDoesNotMatchWithFunctionMetadataErrorCode = "AZFD0013";
         public const string WorkerRuntimeDoesNotMatchWithFunctionMetadataHelpLink = "https://aka.ms/functions-invalid-worker-runtime";
+
+        public const string DeprecatedProxiesErrorCode = "AZFD0014";
+        public const string DeprecatedProxiesHelpLink = "https://aka.ms/functions-deprecated-proxies";
     }
 }

src/WebJobs.Script/Host/ProxyFunctionProvider.cs

@@ -14,6 +14,7 @@
 using Microsoft.Azure.AppService.Proxy.Client;
 using Microsoft.Azure.WebJobs.Logging;
 using Microsoft.Azure.WebJobs.Script.Description;
+using Microsoft.Azure.WebJobs.Script.Diagnostics;
 using Microsoft.Azure.WebJobs.Script.Eventing;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -127,6 +128,12 @@ internal static Collection<ProxyFunctionMetadata> ReadProxyMetadata(string scrip
                 logger.LogInformation("Loading proxies metadata");
                 var metadataCollection = LoadProxyMetadata(proxiesJson, functionErrors, logger);
                 logger.LogInformation($"{metadataCollection.Count} proxies loaded");
+
+                if (metadataCollection.Count > 0)
+                {
+                    logger.LogDiagnosticEventWarning(DiagnosticEventConstants.DeprecatedProxiesErrorCode, "Azure Functions Proxies are deprecated and community support will end on September 30, 2025. Please migrate to Azure API Management or Azure Container Apps. See https://aka.ms/functions-deprecated-proxies for more information.", DiagnosticEventConstants.DeprecatedProxiesHelpLink, null);
+                }
+
                 return metadataCollection;
             }
 

test/WebJobs.Script.Tests/ProxyFunctionProviderTests.cs

@@ -10,6 +10,7 @@
 using System.Threading.Tasks;
 using Microsoft.Azure.WebJobs.Script.Description;
 using Microsoft.Azure.WebJobs.Script.Eventing;
+using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using WebJobs.Script.Tests;
@@ -60,5 +61,48 @@ public async Task ProxyMetadata_WhenProxyFileChanges_IsRefreshed()
                 Assert.Equal(20, proxyMetadata3.Length);
             }
         }
+
+        [Fact]
+        public async Task ProxyFunctionProvider_WhenProxiesEnabled_EmitsDiagnosticWarning()
+        {
+            using (var tempDirectory = new TempDirectory())
+            {
+                var testProxiesPath = Path.Combine(Environment.CurrentDirectory, @"TestScripts\Proxies");
+                var options = new OptionsWrapper<ScriptJobHostOptions>(new ScriptJobHostOptions
+                {
+                    RootScriptPath = tempDirectory.Path
+                });
+
+                var environment = new TestEnvironment(new Dictionary<string, string>
+                {
+                    { EnvironmentSettingNames.AzureWebJobsFeatureFlags, ScriptConstants.FeatureFlagEnableProxies },
+                });
+                var eventManager = new ScriptEventManager();
+                var loggerFactory = new LoggerFactory();
+                var testLogger = new TestLogger("Startup");
+                loggerFactory.AddProvider(new TestLoggerProvider(testLogger));
+
+                var provider = new ProxyFunctionProvider(options, environment, eventManager, loggerFactory);
+
+                // Copy proxies definition to trigger the warning
+                FileUtility.CopyDirectory(testProxiesPath, tempDirectory.Path);
+
+                // Get metadata to trigger loading of proxies and the diagnostic warning
+                ImmutableArray<FunctionMetadata> proxyMetadata = await provider.GetFunctionMetadataAsync();
+
+                // Verify proxies were loaded
+                Assert.NotEmpty(proxyMetadata);
+
+                var warningLog = testLogger.GetLogMessages().FirstOrDefault(m =>
+                    m.Level == LogLevel.Warning &&
+                    m.State is IDictionary<string, object> state &&
+                    state.ContainsKey(ScriptConstants.ErrorCodeKey) &&
+                    state[ScriptConstants.ErrorCodeKey].ToString() == DiagnosticEventConstants.DeprecatedProxiesErrorCode);
+
+                Assert.NotNull(warningLog);
+                Assert.Contains("Azure Functions Proxies are deprecated", warningLog.FormattedMessage);
+                Assert.Contains("September 30, 2025", warningLog.FormattedMessage);
+            }
+        }
     }
 }