Retain Network stack in dual-master

Blue/green deployment of the dual-master recipe requires that the blue
and the green stacks are deployed within the same VPC.

In order to preserve the VPC, the IGW and the subnet upon deletion of
the blue stack, the nested network cloudformation template needs to be
protected from deletion.

Change-Id: I75982a2b02f86dc57ff95ae71e6c326ff88e2717
diff --git a/dual-master/ b/dual-master/
index 359099d..01abceb 100644
--- a/dual-master/
+++ b/dual-master/
@@ -132,6 +132,9 @@
 they will be retained during the stack deletion, so that they can still be used
 by the green stack.
+This includes EFS as well as VPC resources (if they were created as part of the
+blue stack).
 ### Logging
 * All the logs are forwarded to AWS CloudWatch in the LogGroup with the cluster
diff --git a/dual-master/cf-cluster.yml b/dual-master/cf-cluster.yml
index 0c37ad4..841e7e0 100644
--- a/dual-master/cf-cluster.yml
+++ b/dual-master/cf-cluster.yml
@@ -312,6 +312,7 @@
     Type: AWS::CloudFormation::Stack
+    DeletionPolicy: Retain
       TemplateURL: !Join [ '', ['https://', !Ref TemplateBucketName, ''] ]
       TimeoutInMinutes: '25'