(core): improve decoupling dependent stacks (currently can cause deploy failure)

[mikaelstaldal]

What is the problem?

I have a dependency between two stacks (stack A imports X which stack B exports). When I try to remove this dependency (stack A no longer imports X), it break if CDK decides to deploy stack B before stack A.

Reproduction Steps

N/A

What did you expect to happen?

CDK is clever enough to deploy stack A before stack B, and thus removing the import before removing the export.

What actually happened?

CDK deployed stack B before stack A, and deployment failed:

StackB | 0/2 | 8:34:25 AM | UPDATE_ROLLBACK_IN_P | AWS::CloudFormation::Stack                      | Stack B Export StackB:X cannot be deleted as it is in use by StackA

CDK CLI Version

2.12.0 (build c9786db)

Framework Version

No response

Node.js Version

v16.13.0

OS

Linux

Language

Java

Language Version

11

Other information

A workaround is to force a specific deployment order by adding an explicit dependency:

stackB.addDependency(stackA);

[NGL321]

Hey @mikaelstaldal,

Thank you for reporting this issue. It is however hard to determine what the cause of this behavior is from just the information provided.

Could you please clarify with all the steps that resulted in this result as well as indicate why there is a problem arising if "Stack B" is deployed before "Stack A".
When working in the CDK, stack ordering is assumed to be insignificant unless there is a dependency created between stacks (either via imports or explicitly declared). If resources in the former stack depend on resources in the latter, as outlined in our docs you must declare a dependency between those stacks even if no resources are passed between them.

While the Cloudformation and the CDK can intelligently detect most of these dependencies, there are cases where you must explicitly set it:

stackB.node.addDependency(stackA);

Additionally, if you are simply trying to update the stacks from when they had a dependency to not, you may run into trouble that can be resolved by deleting the existing stacks in dependent order, and then redeploying from scratch.

Please let me know if this resolves your problem.

[mikaelstaldal]

OK, maybe it is working as documented. Then this is not a bug, but consider it a feature request, since I believe that it is unreasonably complicated to remove a dependency between stacks.

[NGL321]

That is a fair point. I actually think this is a higher-priority if a request for simplification, so I am converting the issue to a feature-request and bumping its priority for now.

[comcalvi]

This will be resolved by weak references: aws/aws-cdk-rfcs#449

[peterwoodworth]

This is a very well known and documented issue, I don't think we need to track it here anymore

[github-actions]

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[peterwoodworth]

Nevermind, this is a feature request to improve the experience. Reopening