Question

A DevOps team manages a CDK application that synthesizes a parent CloudFormation stack containing several nested stacks. A shared 'NetworkStack' nested stack exports a VPC ID and subnet IDs that are consumed by an 'AppStack' nested stack via CloudFormation cross-stack references (Fn::ImportValue on exported outputs). During a deployment that both changes the CIDR of a subnet in NetworkStack and updates an EC2 launch template in AppStack, the deployment fails with an error that an export cannot be updated because it is in use by another stack. The team needs a reliable pattern to allow the shared network values to change over time without blocking dependent stack updates. Which approach BEST resolves this?

Accepted Answer

Replace the Fn::ImportValue cross-stack references between the nested stacks with direct CDK object references (passing constructs/props), letting CDK pass values as nested stack parameters instead of using account-level exports.

Answer

Add a DeletionPolicy of Retain to the exported resources so CloudFormation does not attempt to delete the exports during the update.

Answer

Split the deployment into two separate pipeline executions, deploying NetworkStack changes first and AppStack changes in a later run, keeping the Fn::ImportValue references.

Answer

Convert the nested stacks into fully independent top-level stacks and use SSM Parameter Store to publish the VPC and subnet IDs, reading them at synth time in AppStack.