fix(ec2): launch template names in imdsv2 not unique across stacks (under feature flag) (#17766)

Fixes #17656

### Notes
Changes the name for the `LaunchTemplate` created in the aspect that enforces IMDSv2 on EC2 instances to a unique name.

Introduces a new feature flag (`@aws-cdk/aws-ec2:uniqueImdsv2TemplateName`) to change the launch template name.

### Testing
Added a unit test

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: jericht

Diff for: packages/@aws-cdk/aws-ec2/lib/aspects/require-imdsv2-aspect.ts

@@ -1,4 +1,6 @@
 import * as cdk from '@aws-cdk/core';
+import { FeatureFlags } from '@aws-cdk/core';
+import * as cxapi from '@aws-cdk/cx-api';
 import { CfnLaunchTemplate } from '../ec2.generated';
 import { Instance } from '../instance';
 import { LaunchTemplate } from '../launch-template';
@@ -83,17 +85,20 @@ export class InstanceRequireImdsv2Aspect extends RequireImdsv2Aspect {
       return;
     }
 
-    const name = `${node.node.id}LaunchTemplate`;
     const launchTemplate = new CfnLaunchTemplate(node, 'LaunchTemplate', {
       launchTemplateData: {
         metadataOptions: {
           httpTokens: 'required',
         },
       },
-      launchTemplateName: name,
     });
+    if (FeatureFlags.of(node).isEnabled(cxapi.EC2_UNIQUE_IMDSV2_LAUNCH_TEMPLATE_NAME)) {
+      launchTemplate.launchTemplateName = cdk.Names.uniqueId(launchTemplate);
+    } else {
+      launchTemplate.launchTemplateName = `${node.node.id}LaunchTemplate`;
+    }
     node.instance.launchTemplate = {
-      launchTemplateName: name,
+      launchTemplateName: launchTemplate.launchTemplateName,
       version: launchTemplate.getAtt('LatestVersionNumber').toString(),
     };
   }

Diff for: packages/@aws-cdk/aws-ec2/test/aspects/require-imdsv2-aspect.test.ts

@@ -4,7 +4,9 @@ import {
   haveResourceLike,
 } from '@aws-cdk/assert-internal';
 import '@aws-cdk/assert-internal/jest';
+import { testFutureBehavior, testLegacyBehavior } from '@aws-cdk/cdk-build-tools';
 import * as cdk from '@aws-cdk/core';
+import * as cxapi from '@aws-cdk/cx-api';
 import {
   CfnLaunchTemplate,
   Instance,
@@ -135,6 +137,57 @@ describe('RequireImdsv2Aspect', () => {
         trace: undefined,
       });
     });
+
+    testFutureBehavior('launch template name is unique with feature flag', { [cxapi.EC2_UNIQUE_IMDSV2_LAUNCH_TEMPLATE_NAME]: true }, cdk.App, (app2) => {
+      // GIVEN
+      const otherStack = new cdk.Stack(app2, 'OtherStack');
+      const otherVpc = new Vpc(otherStack, 'OtherVpc');
+      const otherInstance = new Instance(otherStack, 'OtherInstance', {
+        vpc: otherVpc,
+        instanceType: new InstanceType('t2.micro'),
+        machineImage: MachineImage.latestAmazonLinux(),
+      });
+      const imdsv2Stack = new cdk.Stack(app2, 'RequireImdsv2Stack');
+      const imdsv2Vpc = new Vpc(imdsv2Stack, 'Vpc');
+      const instance = new Instance(imdsv2Stack, 'Instance', {
+        vpc: imdsv2Vpc,
+        instanceType: new InstanceType('t2.micro'),
+        machineImage: MachineImage.latestAmazonLinux(),
+      });
+      const aspect = new InstanceRequireImdsv2Aspect();
+
+      // WHEN
+      cdk.Aspects.of(imdsv2Stack).add(aspect);
+      cdk.Aspects.of(otherStack).add(aspect);
+      app2.synth();
+
+      // THEN
+      const launchTemplate = instance.node.tryFindChild('LaunchTemplate') as LaunchTemplate;
+      const otherLaunchTemplate = otherInstance.node.tryFindChild('LaunchTemplate') as LaunchTemplate;
+      expect(launchTemplate).toBeDefined();
+      expect(otherLaunchTemplate).toBeDefined();
+      expect(launchTemplate.launchTemplateName !== otherLaunchTemplate.launchTemplateName);
+    });
+
+    testLegacyBehavior('launch template name uses legacy id without feature flag', cdk.App, (app2) => {
+      // GIVEN
+      const imdsv2Stack = new cdk.Stack(app2, 'RequireImdsv2Stack');
+      const imdsv2Vpc = new Vpc(imdsv2Stack, 'Vpc');
+      const instance = new Instance(imdsv2Stack, 'Instance', {
+        vpc: imdsv2Vpc,
+        instanceType: new InstanceType('t2.micro'),
+        machineImage: MachineImage.latestAmazonLinux(),
+      });
+      const aspect = new InstanceRequireImdsv2Aspect();
+
+      // WHEN
+      cdk.Aspects.of(imdsv2Stack).add(aspect);
+      app2.synth();
+
+      // THEN
+      const launchTemplate = instance.node.tryFindChild('LaunchTemplate') as LaunchTemplate;
+      expect(launchTemplate.launchTemplateName).toEqual(`${instance.node.id}LaunchTemplate`);
+    });
   });
 
   describe('LaunchTemplateRequireImdsv2Aspect', () => {

Diff for: packages/@aws-cdk/cx-api/lib/features.ts

@@ -178,6 +178,17 @@ export const TARGET_PARTITIONS = '@aws-cdk/core:target-partitions';
  */
 export const ECS_SERVICE_EXTENSIONS_ENABLE_DEFAULT_LOG_DRIVER = '@aws-cdk-containers/ecs-service-extensions:enableDefaultLogDriver';
 
+/**
+ * Enable this feature flag to have Launch Templates generated by the `InstanceRequireImdsv2Aspect` use unique names.
+ *
+ * Previously, the generated Launch Template names were only unique within a stack because they were based only on the
+ * `Instance` construct ID. If another stack that has an `Instance` with the same construct ID is deployed in the same
+ * account and region, the deployments would always fail as the generated Launch Template names were the same.
+ *
+ * The new implementation addresses this issue by generating the Launch Template name with the `Names.uniqueId` method.
+ */
+export const EC2_UNIQUE_IMDSV2_LAUNCH_TEMPLATE_NAME = '@aws-cdk/aws-ec2:uniqueImdsv2TemplateName';
+
 /**
  * This map includes context keys and values for feature flags that enable
  * capabilities "from the future", which we could not introduce as the default
@@ -206,6 +217,7 @@ export const FUTURE_FLAGS: { [key: string]: boolean } = {
   [LAMBDA_RECOGNIZE_VERSION_PROPS]: true,
   [CLOUDFRONT_DEFAULT_SECURITY_POLICY_TLS_V1_2_2021]: true,
   [ECS_SERVICE_EXTENSIONS_ENABLE_DEFAULT_LOG_DRIVER]: true,
+  [EC2_UNIQUE_IMDSV2_LAUNCH_TEMPLATE_NAME]: true,
 
   // We will advertise this flag when the feature is complete
   // [NEW_STYLE_STACK_SYNTHESIS_CONTEXT]: 'true',
@@ -245,6 +257,7 @@ const FUTURE_FLAGS_DEFAULTS: { [key: string]: boolean } = {
   [LAMBDA_RECOGNIZE_VERSION_PROPS]: false,
   [CLOUDFRONT_DEFAULT_SECURITY_POLICY_TLS_V1_2_2021]: false,
   [ECS_SERVICE_EXTENSIONS_ENABLE_DEFAULT_LOG_DRIVER]: false,
+  [EC2_UNIQUE_IMDSV2_LAUNCH_TEMPLATE_NAME]: false,
 };
 
 export function futureFlagDefault(flag: string): boolean | undefined {