fix(kms): aliasName references alias itself (under feature flag) (#25822)

Fixes #25761

The existing behavior was that `alias.aliasName` was always a raw string, so properties like `keyId` and `keyArn` depended on a raw string and not a reference to the alias itself. This behavior is preserved.

Under a new feature flag, `const KMS_ALIAS_NAME_REF = '@aws-cdk/aws-kms:aliasNameRef'`, we instead use a reference to the `aliasName` output itself, which means that properties that depend on `aliasName` now depend on the `alias`. In turn, the `alias` depends on the `key`. This allows the expected behavior where specifying something like `alias.keyArn()` depends on the key.

----

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

Author: kaizencc

packages/aws-cdk-lib/aws-codepipeline/test/artifacts.test.ts

@@ -264,7 +264,6 @@ describe('artifacts', () => {
   });
 });
 
-/* eslint-disable @aws-cdk/no-core-construct */
 function validate(construct: IConstruct): string[] {
   try {
     (construct.node.root as cdk.App).synth();
@@ -276,4 +275,3 @@ function validate(construct: IConstruct): string[] {
     return err.message.split('\n').slice(1);
   }
 }
-/* eslint-enable @aws-cdk/no-core-construct */

packages/aws-cdk-lib/aws-kms/lib/alias.ts

@@ -2,7 +2,8 @@ import { Construct } from 'constructs';
 import { IKey } from './key';
 import { CfnAlias } from './kms.generated';
 import * as iam from '../../aws-iam';
-import { RemovalPolicy, Resource, Stack, Token, Tokenization } from '../../core';
+import { FeatureFlags, RemovalPolicy, Resource, Stack, Token, Tokenization } from '../../core';
+import { KMS_ALIAS_NAME_REF } from '../../cx-api';
 
 const REQUIRED_ALIAS_PREFIX = 'alias/';
 const DISALLOWED_PREFIX = REQUIRED_ALIAS_PREFIX + 'aws/';
@@ -224,7 +225,11 @@ export class Alias extends AliasBase {
       targetKeyId: this.aliasTargetKey.keyArn,
     });
 
-    this.aliasName = this.getResourceNameAttribute(resource.aliasName);
+    if (FeatureFlags.of(this).isEnabled(KMS_ALIAS_NAME_REF)) {
+      this.aliasName = this.getResourceNameAttribute(resource.ref);
+    } else {
+      this.aliasName = this.getResourceNameAttribute(resource.aliasName);
+    }
 
     if (props.removalPolicy) {
       resource.applyRemovalPolicy(props.removalPolicy);

packages/aws-cdk-lib/aws-kms/test/alias.test.ts

@@ -3,6 +3,7 @@ import { Template } from '../../assertions';
 import * as iam from '../../aws-iam';
 import { ArnPrincipal, PolicyStatement } from '../../aws-iam';
 import { App, Aws, CfnOutput, Stack } from '../../core';
+import { KMS_ALIAS_NAME_REF } from '../../cx-api';
 import { Alias } from '../lib/alias';
 import { IKey, Key } from '../lib/key';
 
@@ -110,8 +111,34 @@ test('fails if alias starts with "alias/aws/"', () => {
   })).toThrow(/Alias cannot start with alias\/aws\/: alias\/AWS\/awesome/);
 });
 
+test('keyId includes reference to alias under feature flag', () => {
+  // GIVEN
+  const stack = new Stack();
+  stack.node.setContext(KMS_ALIAS_NAME_REF, true);
+
+  const myKey = new Key(stack, 'MyKey', {
+    enableKeyRotation: true,
+    enabled: true,
+  });
+  const myAlias = new Alias(stack, 'MyAlias', {
+    targetKey: myKey,
+    aliasName: 'alias/myAlias',
+  });
+
+  // WHEN
+  new AliasOutputsConstruct(stack, 'AliasOutputsConstruct', myAlias);
+
+  // THEN - keyId includes reference to the alias itself
+  Template.fromStack(stack).hasOutput('OutId', {
+    Value: {
+      Ref: 'MyAlias9A08CB8C',
+    },
+  });
+});
+
 test('can be used wherever a key is expected', () => {
   const stack = new Stack();
+  stack.node.setContext(KMS_ALIAS_NAME_REF, false);
 
   const myKey = new Key(stack, 'MyKey', {
     enableKeyRotation: true,
@@ -122,21 +149,7 @@ test('can be used wherever a key is expected', () => {
     aliasName: 'alias/myAlias',
   });
 
-  /* eslint-disable @aws-cdk/no-core-construct */
-  class MyConstruct extends Construct {
-    constructor(scope: Construct, id: string, key: IKey) {
-      super(scope, id);
-
-      new CfnOutput(stack, 'OutId', {
-        value: key.keyId,
-      });
-      new CfnOutput(stack, 'OutArn', {
-        value: key.keyArn,
-      });
-    }
-  }
-  new MyConstruct(stack, 'MyConstruct', myAlias);
-  /* eslint-enable @aws-cdk/no-core-construct */
+  new AliasOutputsConstruct(stack, 'AliasOutputsConstruct', myAlias);
 
   Template.fromStack(stack).hasOutput('OutId', {
     Value: 'alias/myAlias',
@@ -161,21 +174,7 @@ test('imported alias by name - can be used where a key is expected', () => {
 
   const myAlias = Alias.fromAliasName(stack, 'MyAlias', 'alias/myAlias');
 
-  /* eslint-disable @aws-cdk/no-core-construct */
-  class MyConstruct extends Construct {
-    constructor(scope: Construct, id: string, key: IKey) {
-      super(scope, id);
-
-      new CfnOutput(stack, 'OutId', {
-        value: key.keyId,
-      });
-      new CfnOutput(stack, 'OutArn', {
-        value: key.keyArn,
-      });
-    }
-  }
-  new MyConstruct(stack, 'MyConstruct', myAlias);
-  /* eslint-enable @aws-cdk/no-core-construct */
+  new AliasOutputsConstruct(stack, 'AliasOutputsConstruct', myAlias);
 
   Template.fromStack(stack).hasOutput('OutId', {
     Value: 'alias/myAlias',
@@ -358,3 +357,15 @@ test('does not add alias if starts with token', () => {
   });
 });
 
+class AliasOutputsConstruct extends Construct {
+  constructor(scope: Construct, id: string, key: IKey) {
+    super(scope, id);
+
+    new CfnOutput(scope, 'OutId', {
+      value: key.keyId,
+    });
+    new CfnOutput(scope, 'OutArn', {
+      value: key.keyArn,
+    });
+  }
+}

packages/aws-cdk-lib/core/lib/feature-flags.ts

@@ -4,7 +4,7 @@ import * as cxapi from '../../cx-api';
 /**
  * Features that are implemented behind a flag in order to preserve backwards
  * compatibility for existing apps. The list of flags are available in the
- * `@aws-cdk/cx-api` module.
+ * `aws-cdk-lib/cx-api` module.
  *
  * The state of the flag for this application is stored as a CDK context variable.
  */

packages/aws-cdk-lib/cx-api/lib/features.ts

@@ -86,6 +86,7 @@ export const REDSHIFT_COLUMN_ID = '@aws-cdk/aws-redshift:columnId';
 export const ENABLE_EMR_SERVICE_POLICY_V2 = '@aws-cdk/aws-stepfunctions-tasks:enableEmrServicePolicyV2';
 export const EC2_RESTRICT_DEFAULT_SECURITY_GROUP = '@aws-cdk/aws-ec2:restrictDefaultSecurityGroup';
 export const APIGATEWAY_REQUEST_VALIDATOR_UNIQUE_ID = '@aws-cdk/aws-apigateway:requestValidatorUniqueId';
+export const KMS_ALIAS_NAME_REF = '@aws-cdk/aws-kms:aliasNameRef';
 
 export const FLAGS: Record<string, FlagInfo> = {
   //////////////////////////////////////////////////////////////////////
@@ -788,6 +789,21 @@ export const FLAGS: Record<string, FlagInfo> = {
     introducedIn: { v2: 'V2·NEXT' },
     recommendedValue: true,
   },
+
+  //////////////////////////////////////////////////////////////////////
+  [KMS_ALIAS_NAME_REF]: {
+    type: FlagType.BugFix,
+    summary: 'KMS Alias name and keyArn will have implicit reference to KMS Key',
+    detailsMd: `
+      This flag allows an implicit dependency to be created between KMS Alias and KMS Key
+      when referencing key.aliasName or key.keyArn.
+
+      If the flag is not set then a raw string is passed as the Alias name and no
+      implicit dependencies will be set.
+    `,
+    introducedIn: { v2: 'V2·NEXT' },
+    recommendedValue: true,
+  },
 };
 
 const CURRENT_MV = 'v2';