fix(redshift-alpha): use same role for database-query singleton function (#32363)

### Issue # (if applicable)

Closes #32089.

### Reason for this change



The Redshift tables use a singleton function as the invoker for various custom resource onEvent Lambda functions. Currently, each custom resource lambda function has a dedicated IAM role to assume. However, since it’s the same singleton function, a shared role could achieve the same outcome.

### Description of changes



Use the same IAM role for the singleton invoker function to assume.

### Description of how you validated changes



deployed to my local stack

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: 5d

packages/@aws-cdk/aws-redshift-alpha/lib/private/database-query.ts

@@ -64,6 +64,7 @@ export class DatabaseQuery<HandlerProps> extends Construct implements iam.IGrant
 
     const provider = new customresources.Provider(this, 'Provider', {
       onEventHandler: handler,
+      role: this.getOrCreateInvokerRole(handler),
     });
 
     const queryHandlerProps: DatabaseQueryHandlerProps & HandlerProps = {
@@ -116,4 +117,19 @@ export class DatabaseQuery<HandlerProps> extends Construct implements iam.IGrant
     }
     return adminUser;
   }
+
+  /**
+   * Get or create the IAM role for the singleton lambda function.
+   * We only need one function since it's just acting as an invoker.
+   * */
+  private getOrCreateInvokerRole(handler: lambda.SingletonFunction): iam.IRole {
+    const id = handler.constructName + 'InvokerRole';
+    const existing = cdk.Stack.of(this).node.tryFindChild(id);
+    return existing != null
+      ? existing as iam.Role
+      : new iam.Role(cdk.Stack.of(this), id, {
+        assumedBy: new iam.ServicePrincipal('lambda.amazonaws.com'),
+        managedPolicies: [iam.ManagedPolicy.fromAwsManagedPolicyName('service-role/AWSLambdaBasicExecutionRole')],
+      });
+  }
 }

packages/@aws-cdk/aws-redshift-alpha/lib/user.ts

@@ -112,6 +112,9 @@ abstract class UserBase extends Construct implements IUser {
         ...this.databaseProps,
         user: this,
       });
+
+      // The privilege should be granted or revoked when the table exists.
+      this.privileges.node.addDependency(table);
     }
 
     this.privileges.addPrivileges(table, ...actions);

packages/@aws-cdk/aws-redshift-alpha/test/database-query.test.ts

@@ -229,4 +229,25 @@ describe('database query', () => {
     expect(stack.resolve(query.getAtt('attribute'))).toStrictEqual({ 'Fn::GetAtt': ['Query435140A1', 'attribute'] });
     expect(stack.resolve(query.getAttString('attribute'))).toStrictEqual({ 'Fn::GetAtt': ['Query435140A1', 'attribute'] });
   });
+
+  it('creates at most one IAM invoker role for handler', () => {
+    new DatabaseQuery(stack, 'Query0', {
+      ...minimalProps,
+    });
+
+    new DatabaseQuery(stack, 'Query1', {
+      ...minimalProps,
+    });
+
+    new DatabaseQuery(stack, 'Query2', {
+      ...minimalProps,
+    });
+
+    const template = Template.fromStack(stack).toJSON();
+    const iamRoles = Object.entries(template.Resources)
+      .map(([k, v]) => [k, Object.getOwnPropertyDescriptor(v, 'Type')?.value])
+      .filter(([k, v]) => v === 'AWS::IAM::Role' && k.toString().includes('InvokerRole'));
+
+    expect(iamRoles.length === 1);
+  });
 });