feat(rds): make VPC optional for serverless Clusters (#17413)

Fixes #17401

----

*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-rds/README.md

@@ -639,7 +639,7 @@ declare const vpc: ec2.Vpc;
 
 const cluster = new rds.ServerlessCluster(this, 'AnotherCluster', {
   engine: rds.DatabaseClusterEngine.AURORA_MYSQL,
-  vpc,
+  vpc, // this parameter is optional for serverless Clusters
   enableDataApi: true, // Optional - will be automatically set if you call grantDataApiAccess()
 });
 
@@ -659,3 +659,11 @@ cluster.grantDataApiAccess(fn);
 **Note**: To invoke the Data API, the resource will need to read the secret associated with the cluster.
 
 To learn more about using the Data API, see the [documentation](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/data-api.html).
+
+### Default VPC
+
+The `vpc` parameter is optional. 
+
+If not provided, the cluster will be created in the default VPC of the account and region.
+As this VPC is not deployed with AWS CDK, you can't configure the `vpcSubnets`, `subnetGroup` or `securityGroups` of the Aurora Serverless Cluster. 
+If you want to provide one of `vpcSubnets`, `subnetGroup` or `securityGroups` parameter, please provide a `vpc`.

packages/@aws-cdk/aws-rds/lib/serverless-cluster.ts

@@ -99,11 +99,14 @@ interface ServerlessClusterNewProps {
 
   /**
    * The VPC that this Aurora Serverless cluster has been created in.
+   *
+   * @default - the default VPC in the account and region will be used
    */
-  readonly vpc: ec2.IVpc;
+  readonly vpc?: ec2.IVpc;
 
   /**
-   * Where to place the instances within the VPC
+   * Where to place the instances within the VPC.
+   * If provided, the `vpc` property must also be specified.
    *
    * @default - the VPC default strategy if not specified.
    */
@@ -129,7 +132,8 @@ interface ServerlessClusterNewProps {
   /**
    * Security group.
    *
-   * @default - a new security group is created.
+   * @default - a new security group is created if `vpc` was provided.
+   *   If the `vpc` property was not provided, no VPC security groups will be associated with the DB cluster.
    */
   readonly securityGroups?: ec2.ISecurityGroup[];
 
@@ -143,7 +147,8 @@ interface ServerlessClusterNewProps {
   /**
    * Existing subnet group for the cluster.
    *
-   * @default - a new subnet group will be created.
+   * @default - a new subnet group is created if `vpc` was provided.
+   *   If the `vpc` property was not provided, no subnet group will be associated with the DB cluster
    */
   readonly subnetGroup?: ISubnetGroup;
 }
@@ -351,19 +356,42 @@ abstract class ServerlessClusterNew extends ServerlessClusterBase {
   constructor(scope: Construct, id: string, props: ServerlessClusterNewProps) {
     super(scope, id);
 
-    const { subnetIds } = props.vpc.selectSubnets(props.vpcSubnets);
-
-    // Cannot test whether the subnets are in different AZs, but at least we can test the amount.
-    if (subnetIds.length < 2) {
-      Annotations.of(this).addError(`Cluster requires at least 2 subnets, got ${subnetIds.length}`);
+    if (props.vpc === undefined) {
+      if (props.vpcSubnets !== undefined) {
+        throw new Error('A VPC is required to use vpcSubnets in ServerlessCluster. Please add a VPC or remove vpcSubnets');
+      }
+      if (props.subnetGroup !== undefined) {
+        throw new Error('A VPC is required to use subnetGroup in ServerlessCluster. Please add a VPC or remove subnetGroup');
+      }
+      if (props.securityGroups !== undefined) {
+        throw new Error('A VPC is required to use securityGroups in ServerlessCluster. Please add a VPC or remove securityGroups');
+      }
     }
 
-    const subnetGroup = props.subnetGroup ?? new SubnetGroup(this, 'Subnets', {
-      description: `Subnets for ${id} database`,
-      vpc: props.vpc,
-      vpcSubnets: props.vpcSubnets,
-      removalPolicy: props.removalPolicy === RemovalPolicy.RETAIN ? props.removalPolicy : undefined,
-    });
+    let subnetGroup: ISubnetGroup | undefined = props.subnetGroup;
+    this.securityGroups = props.securityGroups ?? [];
+    if (props.vpc !== undefined) {
+      const { subnetIds } = props.vpc.selectSubnets(props.vpcSubnets);
+
+      // Cannot test whether the subnets are in different AZs, but at least we can test the amount.
+      if (subnetIds.length < 2) {
+        Annotations.of(this).addError(`Cluster requires at least 2 subnets, got ${subnetIds.length}`);
+      }
+
+      subnetGroup = props.subnetGroup ?? new SubnetGroup(this, 'Subnets', {
+        description: `Subnets for ${id} database`,
+        vpc: props.vpc,
+        vpcSubnets: props.vpcSubnets,
+        removalPolicy: props.removalPolicy === RemovalPolicy.RETAIN ? props.removalPolicy : undefined,
+      });
+
+      this.securityGroups = props.securityGroups ?? [
+        new ec2.SecurityGroup(this, 'SecurityGroup', {
+          description: 'RDS security group',
+          vpc: props.vpc,
+        }),
+      ];
+    }
 
     if (props.backupRetention) {
       const backupRetentionDays = props.backupRetention.toDays();
@@ -379,12 +407,6 @@ abstract class ServerlessClusterNew extends ServerlessClusterBase {
     const clusterParameterGroup = props.parameterGroup ?? clusterEngineBindConfig.parameterGroup;
     const clusterParameterGroupConfig = clusterParameterGroup?.bindToCluster({});
 
-    this.securityGroups = props.securityGroups ?? [
-      new ec2.SecurityGroup(this, 'SecurityGroup', {
-        description: 'RDS security group',
-        vpc: props.vpc,
-      }),
-    ];
 
     const clusterIdentifier = FeatureFlags.of(this).isEnabled(cxapi.RDS_LOWERCASE_DB_IDENTIFIER)
       ? props.clusterIdentifier?.toLowerCase()
@@ -395,7 +417,7 @@ abstract class ServerlessClusterNew extends ServerlessClusterBase {
       databaseName: props.defaultDatabaseName,
       dbClusterIdentifier: clusterIdentifier,
       dbClusterParameterGroupName: clusterParameterGroupConfig?.parameterGroupName,
-      dbSubnetGroupName: subnetGroup.subnetGroupName,
+      dbSubnetGroupName: subnetGroup?.subnetGroupName,
       deletionProtection: defaultDeletionProtection(props.deletionProtection, props.removalPolicy),
       engine: props.engine.engineType,
       engineVersion: props.engine.engineVersion?.fullVersion,
@@ -476,7 +498,7 @@ export class ServerlessCluster extends ServerlessClusterNew {
 
   public readonly secret?: secretsmanager.ISecret;
 
-  private readonly vpc: ec2.IVpc;
+  private readonly vpc?: ec2.IVpc;
   private readonly vpcSubnets?: ec2.SubnetSelection;
 
   private readonly singleUserRotationApplication: secretsmanager.SecretRotationApplication;
@@ -525,6 +547,10 @@ export class ServerlessCluster extends ServerlessClusterNew {
       throw new Error('Cannot add single user rotation for a cluster without secret.');
     }
 
+    if (this.vpc === undefined) {
+      throw new Error('Cannot add single user rotation for a cluster without VPC.');
+    }
+
     const id = 'RotationSingleUser';
     const existing = this.node.tryFindChild(id);
     if (existing) {
@@ -549,6 +575,11 @@ export class ServerlessCluster extends ServerlessClusterNew {
     if (!this.secret) {
       throw new Error('Cannot add multi user rotation for a cluster without secret.');
     }
+
+    if (this.vpc === undefined) {
+      throw new Error('Cannot add multi user rotation for a cluster without VPC.');
+    }
+
     return new secretsmanager.SecretRotation(this, id, {
       ...options,
       excludeCharacters: options.excludeCharacters ?? DEFAULT_PASSWORD_EXCLUDE_CHARS,
@@ -680,4 +711,4 @@ export class ServerlessClusterFromSnapshot extends ServerlessClusterNew {
       this.secret = secret.attach(this);
     }
   }
-}
+}

packages/@aws-cdk/aws-rds/test/integ.serverless-cluster-no-vpc.expected.json

@@ -0,0 +1,18 @@
+{
+  "Resources": {
+    "ServerlessDatabaseWithoutVPC93F9A752": {
+      "Type": "AWS::RDS::DBCluster",
+      "Properties": {
+        "Engine": "aurora-mysql",
+        "DBClusterParameterGroupName": "default.aurora-mysql5.7",
+        "EngineMode": "serverless",
+        "MasterUsername": "admin",
+        "MasterUserPassword": "7959866cacc02c2d243ecfe177464fe6",
+        "StorageEncrypted": true,
+        "VpcSecurityGroupIds": []
+      },
+      "UpdateReplacePolicy": "Delete",
+      "DeletionPolicy": "Delete"
+    }
+  }
+}

packages/@aws-cdk/aws-rds/test/integ.serverless-cluster-no-vpc.ts

@@ -0,0 +1,17 @@
+import * as cdk from '@aws-cdk/core';
+import * as rds from '../lib';
+
+const app = new cdk.App();
+const stack = new cdk.Stack(app, 'aws-cdk-sls-cluster-no-vpc-integ');
+
+const cluster = new rds.ServerlessCluster(stack, 'Serverless Database Without VPC', {
+  engine: rds.DatabaseClusterEngine.AURORA_MYSQL,
+  credentials: {
+    username: 'admin',
+    password: cdk.SecretValue.plainText('7959866cacc02c2d243ecfe177464fe6'),
+  },
+  removalPolicy: cdk.RemovalPolicy.DESTROY,
+});
+cluster.connections.allowDefaultPortFromAnyIpv4('Open to the world');
+
+app.synth();