From 3507155a62e04743d29adf602eb14fa143534730 Mon Sep 17 00:00:00 2001
From: Adam Ruka <adamruka@amazon.com>
Date: Wed, 20 May 2020 16:17:18 -0700
Subject: [PATCH] fix(rds): cannot delete a stack with DbCluster set to
 'Retain'

When the DatabaseCluster has its deletion policy set to 'Retain',
an attempt to delete the stack containing it fails,
as the DbSubnetGroup cannot be removed if it still points to an existing Cluster.
To fix that, set the retention policy of DbSubnetGroup to 'Retain'
if it is 'Retain' on the DatabaseCluster.

Fixes #5282
---
 packages/@aws-cdk/aws-rds/lib/cluster.ts      |  3 +++
 .../@aws-cdk/aws-rds/test/test.cluster.ts     | 24 ++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/packages/@aws-cdk/aws-rds/lib/cluster.ts b/packages/@aws-cdk/aws-rds/lib/cluster.ts
index b3196514f46ce..c80b51068793b 100644
--- a/packages/@aws-cdk/aws-rds/lib/cluster.ts
+++ b/packages/@aws-cdk/aws-rds/lib/cluster.ts
@@ -354,6 +354,9 @@ export class DatabaseCluster extends DatabaseClusterBase {
       dbSubnetGroupDescription: `Subnets for ${id} database`,
       subnetIds,
     });
+    if (props.removalPolicy === RemovalPolicy.RETAIN) {
+      subnetGroup.applyRemovalPolicy(RemovalPolicy.RETAIN);
+    }
 
     const securityGroup = props.instanceProps.securityGroup !== undefined ?
       props.instanceProps.securityGroup : new ec2.SecurityGroup(this, 'SecurityGroup', {
diff --git a/packages/@aws-cdk/aws-rds/test/test.cluster.ts b/packages/@aws-cdk/aws-rds/test/test.cluster.ts
index f2f420d72b415..8d603385c0017 100644
--- a/packages/@aws-cdk/aws-rds/test/test.cluster.ts
+++ b/packages/@aws-cdk/aws-rds/test/test.cluster.ts
@@ -1,4 +1,4 @@
-import { expect, haveResource, ResourcePart, SynthUtils } from '@aws-cdk/assert';
+import { expect, haveResource, haveResourceLike, ResourcePart, SynthUtils } from '@aws-cdk/assert';
 import * as ec2 from '@aws-cdk/aws-ec2';
 import { ManagedPolicy, Role, ServicePrincipal } from '@aws-cdk/aws-iam';
 import * as kms from '@aws-cdk/aws-kms';
@@ -146,6 +146,28 @@ export = {
     test.done();
   },
 
+  "sets the retention policy of the SubnetGroup to 'Retain' if the Cluster is created with 'Retain'"(test: Test) {
+    const stack = new cdk.Stack();
+    const vpc = new ec2.Vpc(stack, 'Vpc');
+
+    new DatabaseCluster(stack, 'Cluster', {
+      masterUser: { username: 'admin' },
+      engine: DatabaseClusterEngine.AURORA,
+      instanceProps: {
+        instanceType: ec2.InstanceType.of(ec2.InstanceClass.M5, ec2.InstanceSize.LARGE),
+        vpc,
+      },
+      removalPolicy: cdk.RemovalPolicy.RETAIN,
+    });
+
+    expect(stack).to(haveResourceLike('AWS::RDS::DBSubnetGroup', {
+      DeletionPolicy: 'Retain',
+      UpdateReplacePolicy: 'Retain',
+    }, ResourcePart.CompleteDefinition));
+
+    test.done();
+  },
+
   'creates a secret when master credentials are not specified'(test: Test) {
     // GIVEN
     const stack = testStack();