feat(s3): custom role for the bucket notifications handler (aws#17794)

Allow users to pass a custom role to `Bucket`, which will be used by the notifications handler.

Fixes aws#9918, aws#13241.

----

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

packages/@aws-cdk/aws-s3/README.md

@@ -249,6 +249,33 @@ const bucket = s3.Bucket.fromBucketAttributes(this, 'ImportedBucket', {
 bucket.addEventNotification(s3.EventType.OBJECT_CREATED, new s3n.SnsDestination(topic));
 ```
 
+When you add an event notification to a bucket, a custom resource is created to 
+manage the notifications. By default, a new role is created for the Lambda
+function that implements this feature. If you want to use your own role instead,
+you should provide it in the `Bucket` constructor:
+
+```ts
+declare const myRole: iam.IRole;
+const bucket = new s3.Bucket(this, 'MyBucket', {
+  notificationsHandlerRole: myRole,
+});
+```
+
+Whatever role you provide, the CDK will try to modify it by adding the 
+permissions from `AWSLambdaBasicExecutionRole` (an AWS managed policy) as well 
+as the permissions `s3:PutBucketNotification` and `s3:GetBucketNotification`. 
+If you’re passing an imported role, and you don’t want this to happen, configure 
+it to be immutable:
+
+```ts
+const importedRole = iam.Role.fromRoleArn(this, 'role', 'arn:aws:iam::123456789012:role/RoleName', {
+  mutable: false,
+});
+```
+
+> If you provide an imported immutable role, make sure that it has at least all 
+> the permissions mentioned above. Otherwise, the deployment will fail!
+
 [S3 Bucket Notifications]: https://docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html
 
 

packages/@aws-cdk/aws-s3/lib/bucket.ts

@@ -427,6 +427,13 @@ export interface BucketAttributes {
    * @default - it's assumed the bucket is in the same region as the scope it's being imported into
    */
   readonly region?: string;
+
+  /**
+   * The role to be used by the notifications handler
+   *
+   * @default - a new role will be created.
+   */
+  readonly notificationsHandlerRole?: iam.IRole;
 }
 
 /**
@@ -484,14 +491,12 @@ export abstract class BucketBase extends Resource implements IBucket {
    */
   protected abstract disallowPublicAccess?: boolean;
 
-  private readonly notifications: BucketNotifications;
+  private notifications?: BucketNotifications;
+
+  protected notificationsHandlerRole?: iam.IRole;
 
   constructor(scope: Construct, id: string, props: ResourceProps = {}) {
     super(scope, id, props);
-
-    // defines a BucketNotifications construct. Notice that an actual resource will only
-    // be added if there are notifications added, so we don't need to condition this.
-    this.notifications = new BucketNotifications(this, 'Notifications', { bucket: this });
   }
 
   /**
@@ -836,7 +841,17 @@ export abstract class BucketBase extends Resource implements IBucket {
    * https://docs.aws.amazon.com/AmazonS3/latest/dev/NotificationHowTo.html
    */
   public addEventNotification(event: EventType, dest: IBucketNotificationDestination, ...filters: NotificationKeyFilter[]) {
-    this.notifications.addNotification(event, dest, ...filters);
+    this.withNotifications(notifications => notifications.addNotification(event, dest, ...filters));
+  }
+
+  private withNotifications(cb: (notifications: BucketNotifications) => void) {
+    if (!this.notifications) {
+      this.notifications = new BucketNotifications(this, 'Notifications', {
+        bucket: this,
+        handlerRole: this.notificationsHandlerRole,
+      });
+    }
+    cb(this.notifications);
   }
 
   /**
@@ -1459,6 +1474,13 @@ export interface BucketProps {
    */
   readonly transferAcceleration?: boolean;
 
+  /**
+   * The role to be used by the notifications handler
+   *
+   * @default - a new role will be created.
+   */
+  readonly notificationsHandlerRole?: iam.IRole;
+
   /**
    * Inteligent Tiering Configurations
    *
@@ -1542,6 +1564,7 @@ export class Bucket extends BucketBase {
       public policy?: BucketPolicy = undefined;
       protected autoCreatePolicy = false;
       protected disallowPublicAccess = false;
+      protected notificationsHandlerRole = attrs.notificationsHandlerRole;
 
       /**
        * Exports this bucket from the stack.
@@ -1629,6 +1652,8 @@ export class Bucket extends BucketBase {
       physicalName: props.bucketName,
     });
 
+    this.notificationsHandlerRole = props.notificationsHandlerRole;
+
     const { bucketEncryption, encryptionKey } = this.parseEncryption(props);
 
     Bucket.validateBucketName(this.physicalName);

packages/@aws-cdk/aws-s3/lib/notifications-resource/notifications-resource-handler.ts

@@ -7,6 +7,10 @@ import * as cdk from '@aws-cdk/core';
 // eslint-disable-next-line no-duplicate-imports, import/order
 import { Construct } from '@aws-cdk/core';
 
+export class NotificationsResourceHandlerProps {
+  role?: iam.IRole;
+}
+
 /**
  * A Lambda-based custom resource handler that provisions S3 bucket
  * notifications for a bucket.
@@ -31,14 +35,14 @@ export class NotificationsResourceHandler extends Construct {
    *
    * @returns The ARN of the custom resource lambda function.
    */
-  public static singleton(context: Construct) {
+  public static singleton(context: Construct, props: NotificationsResourceHandlerProps = {}) {
     const root = cdk.Stack.of(context);
 
     // well-known logical id to ensure stack singletonity
     const logicalId = 'BucketNotificationsHandler050a0587b7544547bf325f094a3db834';
     let lambda = root.node.tryFindChild(logicalId) as NotificationsResourceHandler;
     if (!lambda) {
-      lambda = new NotificationsResourceHandler(root, logicalId);
+      lambda = new NotificationsResourceHandler(root, logicalId, props);
     }
 
     return lambda;
@@ -53,19 +57,19 @@ export class NotificationsResourceHandler extends Construct {
   /**
    * The role of the handler's lambda function.
    */
-  public readonly role: iam.Role;
+  public readonly role: iam.IRole;
 
-  constructor(scope: Construct, id: string) {
+  constructor(scope: Construct, id: string, props: NotificationsResourceHandlerProps = {}) {
     super(scope, id);
 
-    this.role = new iam.Role(this, 'Role', {
+    this.role = props.role ?? new iam.Role(this, 'Role', {
       assumedBy: new iam.ServicePrincipal('lambda.amazonaws.com'),
-      managedPolicies: [
-        iam.ManagedPolicy.fromAwsManagedPolicyName('service-role/AWSLambdaBasicExecutionRole'),
-      ],
     });
 
-    this.role.addToPolicy(new iam.PolicyStatement({
+    this.role.addManagedPolicy(
+      iam.ManagedPolicy.fromAwsManagedPolicyName('service-role/AWSLambdaBasicExecutionRole'),
+    );
+    this.role.addToPrincipalPolicy(new iam.PolicyStatement({
       actions: ['s3:PutBucketNotification'],
       resources: ['*'],
     }));
@@ -95,4 +99,8 @@ export class NotificationsResourceHandler extends Construct {
 
     this.functionArn = resource.getAtt('Arn').toString();
   }
+
+  public addToRolePolicy(statement: iam.PolicyStatement) {
+    this.role.addToPrincipalPolicy(statement);
+  }
 }

packages/@aws-cdk/aws-s3/lib/notifications-resource/notifications-resource.ts

@@ -13,6 +13,11 @@ interface NotificationsProps {
    * The bucket to manage notifications for.
    */
   bucket: IBucket;
+
+  /**
+   * The role to be used by the lambda handler
+   */
+  handlerRole?: iam.IRole;
 }
 
 /**
@@ -36,10 +41,12 @@ export class BucketNotifications extends Construct {
   private readonly topicNotifications = new Array<TopicConfiguration>();
   private resource?: cdk.CfnResource;
   private readonly bucket: IBucket;
+  private readonly handlerRole?: iam.IRole;
 
   constructor(scope: Construct, id: string, props: NotificationsProps) {
     super(scope, id);
     this.bucket = props.bucket;
+    this.handlerRole = props.handlerRole;
   }
 
   /**
@@ -102,12 +109,14 @@ export class BucketNotifications extends Construct {
    */
   private createResourceOnce() {
     if (!this.resource) {
-      const handler = NotificationsResourceHandler.singleton(this);
+      const handler = NotificationsResourceHandler.singleton(this, {
+        role: this.handlerRole,
+      });
 
       const managed = this.bucket instanceof Bucket;
 
       if (!managed) {
-        handler.role.addToPolicy(new iam.PolicyStatement({
+        handler.addToRolePolicy(new iam.PolicyStatement({
           actions: ['s3:GetBucketNotification'],
           resources: ['*'],
         }));

packages/@aws-cdk/aws-s3/test/integ.bucket-auto-delete-objects.expected.json

@@ -110,7 +110,7 @@
       "Properties": {
         "Code": {
           "S3Bucket": {
-            "Ref": "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709S3Bucket2C6C817C"
+            "Ref": "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824S3Bucket09A62232"
           },
           "S3Key": {
             "Fn::Join": [
@@ -123,7 +123,7 @@
                       "Fn::Split": [
                         "||",
                         {
-                          "Ref": "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709S3VersionKeyFA215BD6"
+                          "Ref": "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824S3VersionKeyA28118BE"
                         }
                       ]
                     }
@@ -136,7 +136,7 @@
                       "Fn::Split": [
                         "||",
                         {
-                          "Ref": "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709S3VersionKeyFA215BD6"
+                          "Ref": "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824S3VersionKeyA28118BE"
                         }
                       ]
                     }
@@ -228,7 +228,7 @@
       "Properties": {
         "Code": {
           "S3Bucket": {
-            "Ref": "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfS3BucketE1985B35"
+            "Ref": "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6S3BucketB51EC107"
           },
           "S3Key": {
             "Fn::Join": [
@@ -241,7 +241,7 @@
                       "Fn::Split": [
                         "||",
                         {
-                          "Ref": "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfS3VersionKey610C6DE2"
+                          "Ref": "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6S3VersionKey2B267DB5"
                         }
                       ]
                     }
@@ -254,7 +254,7 @@
                       "Fn::Split": [
                         "||",
                         {
-                          "Ref": "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfS3VersionKey610C6DE2"
+                          "Ref": "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6S3VersionKey2B267DB5"
                         }
                       ]
                     }
@@ -297,29 +297,29 @@
     }
   },
   "Parameters": {
-    "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709S3Bucket2C6C817C": {
+    "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824S3Bucket09A62232": {
       "Type": "String",
-      "Description": "S3 bucket for asset \"84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709\""
+      "Description": "S3 bucket for asset \"be270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824\""
     },
-    "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709S3VersionKeyFA215BD6": {
+    "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824S3VersionKeyA28118BE": {
       "Type": "String",
-      "Description": "S3 key for asset version \"84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709\""
+      "Description": "S3 key for asset version \"be270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824\""
     },
-    "AssetParameters84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709ArtifactHash17D48178": {
+    "AssetParametersbe270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824ArtifactHash76F8FCF2": {
       "Type": "String",
-      "Description": "Artifact hash for asset \"84e9b89449fe2573e51d08cc143e21116ed4608c6db56afffcb4ad85c8130709\""
+      "Description": "Artifact hash for asset \"be270bbdebe0851c887569796e3997437cca54ce86893ed94788500448e92824\""
     },
-    "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfS3BucketE1985B35": {
+    "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6S3BucketB51EC107": {
       "Type": "String",
-      "Description": "S3 bucket for asset \"618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abf\""
+      "Description": "S3 bucket for asset \"31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6\""
     },
-    "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfS3VersionKey610C6DE2": {
+    "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6S3VersionKey2B267DB5": {
       "Type": "String",
-      "Description": "S3 key for asset version \"618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abf\""
+      "Description": "S3 key for asset version \"31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6\""
     },
-    "AssetParameters618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abfArtifactHash467DFC33": {
+    "AssetParameters31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6ArtifactHashEE982197": {
       "Type": "String",
-      "Description": "Artifact hash for asset \"618bbe9863c0edd5c4ca2e24b5063762f020fafec018cd06f57e2bd9f2f48abf\""
+      "Description": "Artifact hash for asset \"31552cb1c5c4cdb0d9502dc59c3cd63cb519dcb7e320e60965c75940297ae3b6\""
     }
   }
 }

packages/@aws-cdk/aws-s3/test/integ.bucket-inventory.expected.json

@@ -155,4 +155,4 @@
       }
     }
   }
-}
+}

packages/@aws-cdk/aws-s3/test/integ.bucket-sharing.lit.expected.json

@@ -71,4 +71,4 @@
       }
     }
   }
-]
+]

packages/@aws-cdk/aws-s3/test/integ.bucket.expected.json

@@ -173,4 +173,4 @@
       }
     }
   }
-}
+}

packages/@aws-cdk/aws-s3/test/integ.bucket.url.lit.expected.json

@@ -44,7 +44,10 @@
           [
             "https://",
             {
-              "Fn::GetAtt": ["MyBucketF68F3FF0", "RegionalDomainName"]
+              "Fn::GetAtt": [
+                "MyBucketF68F3FF0",
+                "RegionalDomainName"
+              ]
             },
             "/myfolder/myfile.txt"
           ]
@@ -58,7 +61,10 @@
           [
             "https://",
             {
-              "Fn::GetAtt": ["MyBucketF68F3FF0", "DomainName"]
+              "Fn::GetAtt": [
+                "MyBucketF68F3FF0",
+                "DomainName"
+              ]
             },
             "/myfolder/myfile.txt"
           ]
@@ -80,4 +86,4 @@
       }
     }
   }
-}
+}