aws · GarrettBeatty · Apr 8, 2026 · Apr 1, 2026 · Apr 1, 2026 · Apr 1, 2026
@@ -0,0 +1,11 @@
+{
+  "Projects": [
+    {
+      "Name": "Amazon.Lambda.Annotations",
+      "Type": "Minor",
+      "ChangelogMessages": [
+        "Added [ALBApi] attribute for configuring Lambda functions as targets behind an Application Load Balancer"
+      ]
+    }
+  ]
+}
@@ -16,7 +16,10 @@
       "test\\TestCustomAuthorizerApp.IntegrationTests\\TestCustomAuthorizerApp.IntegrationTests.csproj",
       "test\\TestServerlessApp.IntegrationTests\\TestServerlessApp.IntegrationTests.csproj",
       "test\\TestServerlessApp.NET8\\TestServerlessApp.NET8.csproj",
-      "test\\TestServerlessApp\\TestServerlessApp.csproj"
+      "src\\Amazon.Lambda.ApplicationLoadBalancerEvents\\Amazon.Lambda.ApplicationLoadBalancerEvents.csproj",
+      "test\\TestServerlessApp\\TestServerlessApp.csproj",
+      "test\\TestServerlessApp.ALB\\TestServerlessApp.ALB.csproj",
+      "test\\TestServerlessApp.ALB.IntegrationTests\\TestServerlessApp.ALB.IntegrationTests.csproj"
     ]
   }
 }
@@ -151,6 +151,10 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestCustomAuthorizerApp.Int
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestCustomAuthorizerApp", "test\TestCustomAuthorizerApp\TestCustomAuthorizerApp.csproj", "{3BFA4B73-BA61-4578-833B-C5B3A16EDA9E}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestServerlessApp.ALB", "test\TestServerlessApp.ALB\TestServerlessApp.ALB.csproj", "{8F7C617D-C611-4DC6-A07C-033F13C1835D}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestServerlessApp.ALB.IntegrationTests", "test\TestServerlessApp.ALB.IntegrationTests\TestServerlessApp.ALB.IntegrationTests.csproj", "{80594C21-C6EB-469E-83CC-68F9F661CA5E}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -941,6 +945,30 @@ Global
 		{3BFA4B73-BA61-4578-833B-C5B3A16EDA9E}.Release|x64.Build.0 = Release|Any CPU
 		{3BFA4B73-BA61-4578-833B-C5B3A16EDA9E}.Release|x86.ActiveCfg = Release|Any CPU
 		{3BFA4B73-BA61-4578-833B-C5B3A16EDA9E}.Release|x86.Build.0 = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|x64.Build.0 = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Debug|x86.Build.0 = Debug|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|x64.ActiveCfg = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|x64.Build.0 = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|x86.ActiveCfg = Release|Any CPU
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D}.Release|x86.Build.0 = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|x64.Build.0 = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Debug|x86.Build.0 = Debug|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|x64.ActiveCfg = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|x64.Build.0 = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|x86.ActiveCfg = Release|Any CPU
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -1015,6 +1043,8 @@ Global
 		{8D03BDF3-7078-4B46-A3F1-C73BE6D6CE0D} = {1DE4EE60-45BA-4EF7-BE00-B9EB861E4C69}
 		{8EEDD576-7FC4-4FAC-A5A2-F58562753A53} = {1DE4EE60-45BA-4EF7-BE00-B9EB861E4C69}
 		{3BFA4B73-BA61-4578-833B-C5B3A16EDA9E} = {1DE4EE60-45BA-4EF7-BE00-B9EB861E4C69}
+		{8F7C617D-C611-4DC6-A07C-033F13C1835D} = {1DE4EE60-45BA-4EF7-BE00-B9EB861E4C69}
+		{80594C21-C6EB-469E-83CC-68F9F661CA5E} = {1DE4EE60-45BA-4EF7-BE00-B9EB861E4C69}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {503678A4-B8D1-4486-8915-405A3E9CF0EB}

@@ -16,3 +16,5 @@ AWSLambda0128 | AWSLambdaCSharpGenerator | Error | Authorizer Payload Version Mi
 AWSLambda0129 | AWSLambdaCSharpGenerator | Error | Missing LambdaFunction Attribute
 AWSLambda0130 | AWSLambdaCSharpGenerator | Error | Invalid return type IAuthorizerResult
 AWSLambda0131 | AWSLambdaCSharpGenerator | Error | FromBody not supported on Authorizer functions
+AWSLambda0132 | AWSLambdaCSharpGenerator | Error | Invalid ALBApiAttribute
+AWSLambda0133 | AWSLambdaCSharpGenerator | Error | ALB Listener Reference Not Found
@@ -242,5 +242,21 @@ public static class DiagnosticDescriptors
             category: "AWSLambdaCSharpGenerator",
             DiagnosticSeverity.Error,
             isEnabledByDefault: true);
+
+        public static readonly DiagnosticDescriptor InvalidAlbApiAttribute = new DiagnosticDescriptor(
+            id: "AWSLambda0132",
+            title: "Invalid ALBApiAttribute",
+            messageFormat: "Invalid ALBApiAttribute encountered: {0}",
+            category: "AWSLambdaCSharpGenerator",
+            DiagnosticSeverity.Error,
+            isEnabledByDefault: true);
+
+        public static readonly DiagnosticDescriptor AlbListenerReferenceNotFound = new DiagnosticDescriptor(
+            id: "AWSLambda0133",
+            title: "ALB Listener Reference Not Found",
+            messageFormat: "The ALBApi ListenerArn references '@{0}', but no resource or parameter named '{0}' was found in the CloudFormation template. Add the listener resource to the template or correct the reference name.",
+            category: "AWSLambdaCSharpGenerator",
+            DiagnosticSeverity.Error,
+            isEnabledByDefault: true);
     }
 }
@@ -0,0 +1,48 @@
+using Amazon.Lambda.Annotations.ALB;
+using Microsoft.CodeAnalysis;
+using System;
+
+namespace Amazon.Lambda.Annotations.SourceGenerator.Models.Attributes
+{
+    /// <summary>
+    /// Builder for <see cref="ALBApiAttribute"/>.
+    /// </summary>
+    public class ALBApiAttributeBuilder
+    {
+        public static ALBApiAttribute Build(AttributeData att)
+        {
+            if (att.ConstructorArguments.Length != 3)
+            {
+                throw new NotSupportedException($"{TypeFullNames.ALBApiAttribute} must have constructor with 3 arguments.");
+            }
+
+            var listenerArn = att.ConstructorArguments[0].Value as string;
+            var pathPattern = att.ConstructorArguments[1].Value as string;
+            var priority = (int)att.ConstructorArguments[2].Value;
+
+            var data = new ALBApiAttribute(listenerArn, pathPattern, priority);
+
+            foreach (var pair in att.NamedArguments)
+            {
+                if (pair.Key == nameof(data.MultiValueHeaders) && pair.Value.Value is bool multiValueHeaders)
+                {
+                    data.MultiValueHeaders = multiValueHeaders;
+                }
+                else if (pair.Key == nameof(data.HostHeader) && pair.Value.Value is string hostHeader)
+                {
+                    data.HostHeader = hostHeader;
+                }
+                else if (pair.Key == nameof(data.HttpMethod) && pair.Value.Value is string httpMethod)
+                {
+                    data.HttpMethod = httpMethod;
+                }
+                else if (pair.Key == nameof(data.ResourceName) && pair.Value.Value is string resourceName)
+                {
+                    data.ResourceName = resourceName;
+                }
+            }
+
+            return data;
+        }
+    }
+}
@@ -1,4 +1,5 @@
 using System;
+using Amazon.Lambda.Annotations.ALB;
 using Amazon.Lambda.Annotations.APIGateway;
 using Amazon.Lambda.Annotations.SQS;
 using Microsoft.CodeAnalysis;
@@ -108,6 +109,15 @@ public static AttributeModel Build(AttributeData att, GeneratorExecutionContext
                     Type = TypeModelBuilder.Build(att.AttributeClass, context)
                 };
             }
+            else if (att.AttributeClass.Equals(context.Compilation.GetTypeByMetadataName(TypeFullNames.ALBApiAttribute), SymbolEqualityComparer.Default))
+            {
+                var data = ALBApiAttributeBuilder.Build(att);
+                model = new AttributeModel<ALBApiAttribute>
+                {
+                    Data = data,
+                    Type = TypeModelBuilder.Build(att.AttributeClass, context)
+                };
+            }
             else
             {
                 model = new AttributeModel

@@ -11,6 +11,7 @@ public enum EventType
         SQS,
         DynamoDB,
         Schedule,
-        Authorizer
+        Authorizer,
+        ALB
     }
 }
@@ -31,6 +31,10 @@ public static HashSet<EventType> Build(IMethodSymbol lambdaMethodSymbol,
                 {
                     events.Add(EventType.Authorizer);
                 }
+                else if (attribute.AttributeClass.ToDisplayString() == TypeFullNames.ALBApiAttribute)
+                {
+                    events.Add(EventType.ALB);
+                }
             }
 
             return events;

@@ -130,6 +130,20 @@ private static TypeModel BuildResponseType(IMethodSymbol lambdaMethodSymbol,
                         throw new ArgumentOutOfRangeException();
                 }
             }
+            else if (lambdaMethodSymbol.HasAttribute(context, TypeFullNames.ALBApiAttribute))
+            {
+                // ALB functions return ApplicationLoadBalancerResponse
+                // If the user already returns ApplicationLoadBalancerResponse, pass through the return type.
+                // Otherwise, wrap in ApplicationLoadBalancerResponse.
+                if (lambdaMethodModel.ReturnsApplicationLoadBalancerResponse)
+                {
+                    return lambdaMethodModel.ReturnType;
+                }
+                var symbol = lambdaMethodModel.ReturnsVoidOrGenericTask ?
+                    task.Construct(context.Compilation.GetTypeByMetadataName(TypeFullNames.ApplicationLoadBalancerResponse)):
+                    context.Compilation.GetTypeByMetadataName(TypeFullNames.ApplicationLoadBalancerResponse);
+                return TypeModelBuilder.Build(symbol, context);
+            }
             else
             {
                 return lambdaMethodModel.ReturnType;

@@ -89,6 +89,31 @@ public bool ReturnsIAuthorizerResult
             }
         }
 
+        /// <summary>
+        /// Returns true if the Lambda function returns either ApplicationLoadBalancerResponse or Task&lt;ApplicationLoadBalancerResponse&gt;
+        /// </summary>
+        public bool ReturnsApplicationLoadBalancerResponse
+        {
+            get
+            {
+                if (ReturnsVoid)
+                {
+                    return false;
+                }
+
+                if (ReturnType.FullName == TypeFullNames.ApplicationLoadBalancerResponse)
+                {
+                    return true;
+                }
+                if (ReturnsGenericTask && ReturnType.TypeArguments.Count == 1 && ReturnType.TypeArguments[0].FullName == TypeFullNames.ApplicationLoadBalancerResponse)
+                {
+                    return true;
+                }
+
+                return false;
+            }
+        }
+
         /// <summary>
         /// Returns true if the Lambda function returns either void, Task, SQSBatchResponse or Task<SQSBatchResponse>
         /// </summary>

@@ -21,7 +21,8 @@ internal class SyntaxReceiver : ISyntaxContextReceiver
             { "RestApiAuthorizerAttribute", "RestApiAuthorizer" },
             { "HttpApiAttribute", "HttpApi" },
             { "RestApiAttribute", "RestApi" },
-            { "SQSEventAttribute", "SQSEvent" }
+            { "SQSEventAttribute", "SQSEvent" },
+            { "ALBApiAttribute", "ALBApi" }
         };
 
         public List<MethodDeclarationSyntax> LambdaMethods { get; } = new List<MethodDeclarationSyntax>();

@@ -46,6 +46,10 @@ public static class TypeFullNames
         public const string SQSBatchResponse = "Amazon.Lambda.SQSEvents.SQSBatchResponse";
         public const string SQSEventAttribute = "Amazon.Lambda.Annotations.SQS.SQSEventAttribute";
 
+        public const string ApplicationLoadBalancerRequest = "Amazon.Lambda.ApplicationLoadBalancerEvents.ApplicationLoadBalancerRequest";
+        public const string ApplicationLoadBalancerResponse = "Amazon.Lambda.ApplicationLoadBalancerEvents.ApplicationLoadBalancerResponse";
+        public const string ALBApiAttribute = "Amazon.Lambda.Annotations.ALB.ALBApiAttribute";
+
         public const string LambdaSerializerAttribute = "Amazon.Lambda.Core.LambdaSerializerAttribute";
         public const string DefaultLambdaSerializer = "Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer";
 
@@ -63,11 +67,17 @@ public static class TypeFullNames
             APIGatewayCustomAuthorizerRequest
         };
 
+        public static HashSet<string> ALBRequests = new HashSet<string>
+        {
+            ApplicationLoadBalancerRequest
+        };
+
         public static HashSet<string> Events = new HashSet<string>
         {
             RestApiAttribute,
             HttpApiAttribute,
-            SQSEventAttribute
+            SQSEventAttribute,
+            ALBApiAttribute
         };
     }
 }
@@ -1,4 +1,5 @@
-using Amazon.Lambda.Annotations.SourceGenerator.Diagnostics;
+using Amazon.Lambda.Annotations.ALB;
+using Amazon.Lambda.Annotations.SourceGenerator.Diagnostics;
 using Amazon.Lambda.Annotations.SourceGenerator.Extensions;
 using Amazon.Lambda.Annotations.SourceGenerator.Models;
 using Amazon.Lambda.Annotations.SourceGenerator.Models.Attributes;
@@ -59,6 +60,7 @@ internal static bool ValidateFunction(GeneratorExecutionContext context, IMethod
             // Validate Events
             ValidateApiGatewayEvents(lambdaFunctionModel, methodLocation, diagnostics);
             ValidateSqsEvents(lambdaFunctionModel, methodLocation, diagnostics);
+            ValidateAlbEvents(lambdaFunctionModel, methodLocation, diagnostics);
 
             return ReportDiagnostics(diagnosticReporter, diagnostics);
         }
@@ -86,6 +88,16 @@ internal static bool ValidateDependencies(GeneratorExecutionContext context, IMe
                 }
             }
 
+            // Check for references to "Amazon.Lambda.ApplicationLoadBalancerEvents" if the Lambda method is annotated with ALBApi attribute.
+            if (lambdaMethodSymbol.HasAttribute(context, TypeFullNames.ALBApiAttribute))
+            {
+                if (context.Compilation.ReferencedAssemblyNames.FirstOrDefault(x => x.Name == "Amazon.Lambda.ApplicationLoadBalancerEvents") == null)
+                {
+                    diagnosticReporter.Report(Diagnostic.Create(DiagnosticDescriptors.MissingDependencies, methodLocation, "Amazon.Lambda.ApplicationLoadBalancerEvents"));
+                    return false;
+                }
+            }
+
             return true;
         }
 
@@ -268,6 +280,48 @@ private static void ValidateSqsEvents(LambdaFunctionModel lambdaFunctionModel, L
             }
         }
 
+        private static void ValidateAlbEvents(LambdaFunctionModel lambdaFunctionModel, Location methodLocation, List<Diagnostic> diagnostics)
+        {
+            // If the method does not contain any ALB events, then simply return early
+            if (!lambdaFunctionModel.LambdaMethod.Events.Contains(EventType.ALB))
+            {
+                return;
+            }
+
+            // Validate ALBApiAttributes
+            foreach (var att in lambdaFunctionModel.Attributes)
+            {
+                if (att.Type.FullName != TypeFullNames.ALBApiAttribute)
+                    continue;
+
+                var albApiAttribute = ((AttributeModel<ALBApiAttribute>)att).Data;
+                var validationErrors = albApiAttribute.Validate();
+                validationErrors.ForEach(errorMessage => diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InvalidAlbApiAttribute, methodLocation, errorMessage)));
+            }
+
+            // Validate method parameters - When using ALBApiAttribute, the method signature must be
+            // (ApplicationLoadBalancerRequest request) or (ApplicationLoadBalancerRequest request, ILambdaContext context)
+            var parameters = lambdaFunctionModel.LambdaMethod.Parameters;
+            if (parameters.Count == 0 ||
+                parameters.Count > 2 ||
+                (parameters.Count == 1 && parameters[0].Type.FullName != TypeFullNames.ApplicationLoadBalancerRequest) ||
+                (parameters.Count == 2 && (parameters[0].Type.FullName != TypeFullNames.ApplicationLoadBalancerRequest || parameters[1].Type.FullName != TypeFullNames.ILambdaContext)))
+            {
+                var errorMessage = $"When using the {nameof(ALBApiAttribute)}, the Lambda method can accept at most 2 parameters. " +
+                    $"The first parameter is required and must be of type {TypeFullNames.ApplicationLoadBalancerRequest}. " +
+                    $"The second parameter is optional and must be of type {TypeFullNames.ILambdaContext}.";
+                diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InvalidLambdaMethodSignature, methodLocation, errorMessage));
+            }
+
+            // Validate method return type - When using ALBApiAttribute, the return type must be
+            // ApplicationLoadBalancerResponse or Task<ApplicationLoadBalancerResponse>
+            if (!lambdaFunctionModel.LambdaMethod.ReturnsApplicationLoadBalancerResponse)
+            {
+                var errorMessage = $"When using the {nameof(ALBApiAttribute)}, the Lambda method must return {TypeFullNames.ApplicationLoadBalancerResponse} or Task<{TypeFullNames.ApplicationLoadBalancerResponse}>";
+                diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InvalidLambdaMethodSignature, methodLocation, errorMessage));
+            }
+        }
+
         private static bool ReportDiagnostics(DiagnosticReporter diagnosticReporter, List<Diagnostic> diagnostics)
         {
             var isValid = true;