chore(elasticloadbalancingv2): add warning for missing ApplicationTargetGroup protocol

packages/aws-cdk-lib/aws-elasticloadbalancingv2/README.md

@@ -609,6 +609,7 @@ declare const vpc: ec2.Vpc;
 const tg1 = new elbv2.ApplicationTargetGroup(this, 'TG1', {
   targetType: elbv2.TargetType.INSTANCE,
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   stickinessCookieDuration: Duration.minutes(5),
   vpc,
 });
@@ -617,6 +618,7 @@ const tg1 = new elbv2.ApplicationTargetGroup(this, 'TG1', {
 const tg2 = new elbv2.ApplicationTargetGroup(this, 'TG2', {
   targetType: elbv2.TargetType.INSTANCE,
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   stickinessCookieDuration: Duration.minutes(5),
   stickinessCookieName: 'MyDeliciousCookie',
   vpc,
@@ -639,6 +641,7 @@ const tg = new elbv2.ApplicationTargetGroup(this, 'TG', {
   targetType: elbv2.TargetType.INSTANCE,
   slowStart: Duration.seconds(60),
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   vpc,
 });
 ```
@@ -680,6 +683,7 @@ declare const vpc: ec2.Vpc;
 
 const tg = new elbv2.ApplicationTargetGroup(this, 'TargetGroup', {
   vpc,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   loadBalancingAlgorithmType: elbv2.TargetGroupLoadBalancingAlgorithmType.WEIGHTED_RANDOM,
   enableAnomalyMitigation: true,
 });
@@ -699,6 +703,7 @@ declare const vpc: ec2.Vpc;
 const targetGroup = new elbv2.ApplicationTargetGroup(this, 'TargetGroup', {
   vpc,
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   targetType: elbv2.TargetType.INSTANCE,
 
   // Whether cross zone load balancing is enabled.
@@ -720,13 +725,15 @@ declare const vpc: ec2.Vpc;
 const ipv4ApplicationTargetGroup = new elbv2.ApplicationTargetGroup(this, 'IPv4ApplicationTargetGroup', {
   vpc,
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   targetType: elbv2.TargetType.INSTANCE,
   ipAddressType: elbv2.TargetGroupIpAddressType.IPV4,
 });
 
 const ipv6ApplicationTargetGroup = new elbv2.ApplicationTargetGroup(this, 'Ipv6ApplicationTargetGroup', {
   vpc,
   port: 80,
+  protocol: elbv2.ApplicationProtocol.HTTP,
   targetType: elbv2.TargetType.INSTANCE,
   ipAddressType: elbv2.TargetGroupIpAddressType.IPV6,
 });

packages/aws-cdk-lib/aws-elasticloadbalancingv2/lib/alb/application-target-group.ts

@@ -614,9 +614,18 @@ export class ApplicationTargetGroup extends TargetGroupBase implements IApplicat
   protected validateTargetGroup(): string[] {
     const ret = super.validateTargetGroup();
 
+    // Check if this is a Lambda target group (either explicitly set or will be set to Lambda)
+    const isLambdaTarget = this.targetType === TargetType.LAMBDA;
+
+    // For non-Lambda target groups, protocol is required
+    if (!isLambdaTarget && this.protocol === undefined) {
+      ret.push('Protocol is required for ApplicationTargetGroup');
+    }
+
+    // Port validation for when targets are added (existing logic for non-Lambda)
     if (this.targetType !== undefined && this.targetType !== TargetType.LAMBDA
-      && (this.protocol === undefined || this.port === undefined)) {
-      ret.push('At least one of \'port\' or \'protocol\' is required for a non-Lambda TargetGroup');
+      && this.port === undefined) {
+      ret.push('Port is required for non-Lambda TargetGroup');
     }
 
     if (this.healthCheck) {

packages/aws-cdk-lib/aws-elasticloadbalancingv2/test/alb/listener.test.ts

@@ -1430,11 +1430,13 @@ describe('tests', () => {
     const listener = lb.addListener('Listener', {
       port: 443,
       certificates: [importedCertificate(stack, 'cert1'), importedCertificate(stack, 'cert2')],
-      defaultTargetGroups: [new elbv2.ApplicationTargetGroup(stack, 'Group', { vpc, port: 80 })],
+      defaultTargetGroups: [new elbv2.ApplicationTargetGroup(stack, 'Group', { vpc, port: 80, protocol: elbv2.ApplicationProtocol.HTTP })],
     });
 
     listener.addTargets('Target1', {
       priority: 10,
+      port: 80,
+      protocol: elbv2.ApplicationProtocol.HTTP,
       conditions: [elbv2.ListenerCondition.pathPatterns(['/test/path/1', '/test/path/2'])],
     });
 
@@ -1476,7 +1478,7 @@ describe('tests', () => {
     const stack = new cdk.Stack();
     const vpc = new ec2.Vpc(stack, 'Stack');
     const lb = new elbv2.ApplicationLoadBalancer(stack, 'LB', { vpc });
-    const group1 = new elbv2.ApplicationTargetGroup(stack, 'Group1', { vpc, port: 80 });
+    const group1 = new elbv2.ApplicationTargetGroup(stack, 'Group1', { vpc, port: 80, protocol: elbv2.ApplicationProtocol.HTTP });
     const group2 = new elbv2.ApplicationTargetGroup(stack, 'Group2', { vpc, port: 81, protocol: elbv2.ApplicationProtocol.HTTP });
 
     // WHEN

packages/aws-cdk-lib/aws-elasticloadbalancingv2/test/alb/target-group.test.ts

@@ -77,6 +77,73 @@ describe('tests', () => {
     expect(() => app.synth()).toThrow(/port\/protocol should not be specified for Lambda targets/);
   });
 
+  test('ApplicationTargetGroup requires protocol when no targets added', () => {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'Stack');
+    const vpc = new ec2.Vpc(stack, 'Vpc');
+
+    // WHEN - Create ApplicationTargetGroup without protocol or port
+    new elbv2.ApplicationTargetGroup(stack, 'TG', {
+      vpc,
+      // protocol and port are both missing
+    });
+
+    // THEN
+    expect(() => app.synth()).toThrow(/Protocol is required for ApplicationTargetGroup/);
+  });
+
+  test('ApplicationTargetGroup with protocol should not throw validation error', () => {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'Stack');
+    const vpc = new ec2.Vpc(stack, 'Vpc');
+
+    // WHEN - Create ApplicationTargetGroup with protocol
+    new elbv2.ApplicationTargetGroup(stack, 'TG', {
+      vpc,
+      port: 80,
+      protocol: elbv2.ApplicationProtocol.HTTP,
+    });
+
+    // THEN - Should not throw
+    expect(() => app.synth()).not.toThrow();
+  });
+
+  test('ApplicationTargetGroup with Lambda target does not require protocol', () => {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'Stack');
+
+    // WHEN - Create ApplicationTargetGroup for Lambda without protocol
+    new elbv2.ApplicationTargetGroup(stack, 'TG', {
+      targetType: elbv2.TargetType.LAMBDA,
+      // protocol is missing but should be allowed for Lambda
+    });
+
+    // THEN - Should not throw
+    expect(() => app.synth()).not.toThrow();
+  });
+
+  test('ApplicationTargetGroup requires protocol even when targets added later', () => {
+    // GIVEN
+    const app = new cdk.App();
+    const stack = new cdk.Stack(app, 'Stack');
+    const vpc = new ec2.Vpc(stack, 'Vpc');
+
+    // WHEN - Create ApplicationTargetGroup without protocol or port, then add non-Lambda target
+    const tg = new elbv2.ApplicationTargetGroup(stack, 'TG', {
+      vpc,
+      // protocol and port are both missing
+    });
+
+    // Add a non-Lambda target
+    tg.addTarget(new elbv2.InstanceTarget('i-1234'));
+
+    // THEN - Should still require protocol
+    expect(() => app.synth()).toThrow(/Protocol is required for ApplicationTargetGroup/);
+  });
+
   test('Can add self-registering target to imported TargetGroup', () => {
     // GIVEN
     const app = new cdk.App();
@@ -157,6 +224,7 @@ describe('tests', () => {
     new elbv2.ApplicationTargetGroup(stack, 'Group', {
       vpc,
       ipAddressType,
+      protocol: elbv2.ApplicationProtocol.HTTP,
     });
 
     Template.fromStack(stack).hasResourceProperties('AWS::ElasticLoadBalancingV2::TargetGroup', {
@@ -174,6 +242,7 @@ describe('tests', () => {
     new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
       stickinessCookieDuration: cdk.Duration.minutes(5),
       vpc,
+      protocol: elbv2.ApplicationProtocol.HTTP,
     });
 
     // THEN
@@ -206,6 +275,7 @@ describe('tests', () => {
       stickinessCookieDuration: cdk.Duration.minutes(5),
       stickinessCookieName: 'MyDeliciousCookie',
       vpc,
+      protocol: elbv2.ApplicationProtocol.HTTP,
     });
 
     // THEN
@@ -241,6 +311,7 @@ describe('tests', () => {
     new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
       loadBalancingAlgorithmType: elbv2.TargetGroupLoadBalancingAlgorithmType.LEAST_OUTSTANDING_REQUESTS,
       vpc,
+      protocol: elbv2.ApplicationProtocol.HTTP,
     });
 
     // THEN
@@ -267,6 +338,7 @@ describe('tests', () => {
     // WHEN
     new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
       vpc,
+      protocol: elbv2.ApplicationProtocol.HTTP,
       protocolVersion: elbv2.ApplicationProtocolVersion.GRPC,
       healthCheck: {
         enabled: true,
@@ -370,6 +442,7 @@ describe('tests', () => {
     new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
       slowStart: cdk.Duration.seconds(0),
       vpc,
+      protocol: elbv2.ApplicationProtocol.HTTP,
     });
 
     // THEN
@@ -442,6 +515,7 @@ describe('tests', () => {
       // WHEN
       new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
         vpc,
+        protocol: elbv2.ApplicationProtocol.HTTP,
         healthCheck: {
           protocol: protocol,
         },
@@ -462,6 +536,7 @@ describe('tests', () => {
       const vpc = new ec2.Vpc(stack, 'VPC', {});
       const tg = new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
         vpc,
+        protocol: elbv2.ApplicationProtocol.HTTP,
       });
 
       // WHEN
@@ -737,6 +812,7 @@ describe('tests', () => {
       new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
         loadBalancingAlgorithmType: elbv2.TargetGroupLoadBalancingAlgorithmType.WEIGHTED_RANDOM,
         vpc,
+        protocol: elbv2.ApplicationProtocol.HTTP,
         enableAnomalyMitigation: true,
       });
 
@@ -769,6 +845,7 @@ describe('tests', () => {
       new elbv2.ApplicationTargetGroup(stack, 'TargetGroup', {
         loadBalancingAlgorithmType: elbv2.TargetGroupLoadBalancingAlgorithmType.WEIGHTED_RANDOM,
         vpc,
+        protocol: elbv2.ApplicationProtocol.HTTP,
         enableAnomalyMitigation: false,
       });
 
@@ -831,7 +908,7 @@ describe('tests', () => {
       const vpc = new ec2.Vpc(stack, 'VPC', {});
 
       // WHEN
-      new elbv2.ApplicationTargetGroup(stack, 'LB', { crossZoneEnabled, vpc });
+      new elbv2.ApplicationTargetGroup(stack, 'LB', { crossZoneEnabled, vpc, protocol: elbv2.ApplicationProtocol.HTTP });
 
       Template.fromStack(stack).hasResourceProperties('AWS::ElasticLoadBalancingV2::TargetGroup', {
         TargetGroupAttributes: [