feat(core): `stack.exportValue()` can be used to solve "deadly embrace" #12778

rix0rrr · 2021-01-29T17:26:32Z

Deadly embrace (<3 who came up with this term) is an issue where a consumer
stack depends on a producer stack via CloudFormation Exports, and you want to
remove the use from the consumer.

Removal of the resource sharing implicitly removes the CloudFormation Export,
but now CloudFormation won't let you deploy that because the deployment order
is always forced to be (1st) producer (2nd) consumer, and when the producer deploys
and tries to remove the Export, the consumer is still using it.

The best way to work around it is to manually ensure the CloudFormation Export
exists while you remove the consuming relationship. @skinny85 has a blog
post about this, but the mechanism can be more smooth.

Add a method, stack.exportValue(...) which can be used to
create the Export for the duration of the deployment that breaks
the relationship, and add an explanation of how to use it.

Genericize the method a bit so it also solves a long-standing issue about no L2 support for exports.

Fixes #7602, fixes #2036.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

"Deadly embrace" is a great term but an annoying problem. The best way to work around it is to manually ensure the CloudFormation Export exists while you remove the consuming relationship. Adam has a blog post about this, but the mechanism can be more smooth. Add a method, `stack.exportAttribute(...)` which can be used to create the Export for the duration of the deployment that breaks the relationship, and add an explanation of how to use it. Fixes #7602.

gitpod-io · 2021-01-29T17:26:35Z

packages/@aws-cdk/core/README.md

packages/@aws-cdk/core/lib/stack.ts

eladb · 2021-01-31T09:30:40Z

packages/@aws-cdk/core/lib/token.ts

+   *
+   * In case of a string, the string must not be a concatenation.
+   */
+  public static reverse(x: any): IResolvable | undefined {


I am not 100% sure this has tons of value as a public API. Can we make it internal for now?

Not really. If we want to use it in other modules, it needs to be public (Adam's needed this when implementing a guard that reverses Tokens in CodeBuild, but ended up reimplementing himself).

Plus, it seems only fair that if the API to encode a token to a literal is public, the API to reverse that encoding should also be public.

eladb · 2021-01-31T09:33:27Z

packages/@aws-cdk/core/README.md

@@ -92,6 +92,36 @@ nested stack and referenced using `Fn::GetAtt "Outputs.Xxx"` from the parent.

 Nested stacks also support the use of Docker image and file assets.

+### Breaking automatic references


Feels like this should be part of the section that describes cross references in the dev guide.

Maybe we can copy the contents from the dev guide to here and just add this as a subsection? And then also duplicate this to the dev guide?

Co-authored-by: Elad Ben-Israel <[email protected]>

eladb · 2021-02-01T10:53:14Z

packages/@aws-cdk/core/lib/stack.ts

+   * - Don't forget to remove the `exportAttribute()` call as well.
+   * - Deploy again (this time only the `producerStack` will be changed -- the bucket will be deleted).
+   */
+  public exportAttribute(exportedAttribute: any) {


As discussed, I am wondering if we can make this slightly more generic and resolve #2036 along the way:

const importValue = stack.exportValue(attribute); // auto-name const importValue = stack.exportValue(1234, { name: 'my-export-name' }); // since the value is not an attribute `name` is required

mergify · 2021-02-01T13:03:49Z

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mergify · 2021-02-01T14:17:40Z

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

aws-cdk-automation · 2021-02-01T14:17:57Z

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henrist · 2021-02-01T15:17:34Z

packages/@aws-cdk/core/README.md

+- Make sure `stack2` no longer references `bucket.bucketName` (maybe the consumer
+  stack now uses its own bucket, or it writes to an AWS DynamoDB table, or maybe you just
+  remove the Lambda Function altogether).
+- In the `stack1` class, call `this.exportAttribute(this.bucket.bucketName)`. This


Seems the duplicate docs (readme + tsdoc) got out-of-sync during review/changes, e.g. this should be exportValue

@skinny85

…e" (aws#12778) Deadly embrace (<3 who came up with this term) is an issue where a consumer stack depends on a producer stack via CloudFormation Exports, and you want to remove the use from the consumer. Removal of the resource sharing implicitly removes the CloudFormation Export, but now CloudFormation won't let you deploy that because the deployment order is always forced to be (1st) producer (2nd) consumer, and when the producer deploys and tries to remove the Export, the consumer is still using it. The best way to work around it is to manually ensure the CloudFormation Export exists while you remove the consuming relationship. @skinny85 has a [blog post] about this, but the mechanism can be more smooth. Add a method, `stack.exportValue(...)` which can be used to create the Export for the duration of the deployment that breaks the relationship, and add an explanation of how to use it. Genericize the method a bit so it also solves a long-standing issue about no L2 support for exports. Fixes aws#7602, fixes aws#2036. [blog post]: https://www.endoflineblog.com/cdk-tips-03-how-to-unblock-cross-stack-references ---- *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

CDK has a limitation where if you attempt to remove all references to a resource from another stack, CDK will attempt to remove the export for that resource, which then fails because it sees there is still an external dependency on that resource, creating a 'deadly embrace' See aws/aws-cdk#12778. The workaround for this is to set dummy export values to trick CDK into keeping the unused exports around until you've deployed your updates to the dependent stack.

rix0rrr requested a review from a team January 29, 2021 17:26

rix0rrr self-assigned this Jan 29, 2021

github-actions bot added the @aws-cdk/core Related to core CDK functionality label Jan 29, 2021

mergify bot added the contribution/core This is a PR that came from AWS. label Jan 29, 2021

rix0rrr changed the title ~~feat(core): manually control exports to solve "deadly embrace"~~ feat(core): manual control of Exports solves "deadly embrace" Jan 29, 2021

eladb reviewed Jan 31, 2021

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rix0rrr and others added 4 commits February 1, 2021 09:28

Update packages/@aws-cdk/core/README.md

cd0fbe1

Co-authored-by: Elad Ben-Israel <[email protected]>

Update packages/@aws-cdk/core/README.md

c37632f

Co-authored-by: Elad Ben-Israel <[email protected]>

Update packages/@aws-cdk/core/lib/stack.ts

d1091fa

Co-authored-by: Elad Ben-Israel <[email protected]>

Touch up README, fix build

7ff16d1

eladb reviewed Feb 1, 2021

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eladb added the pr/do-not-merge This PR should not be merged at this time. label Feb 1, 2021

rix0rrr changed the title ~~feat(core): manual control of Exports solves "deadly embrace"~~ feat(core): stack.exportValue() can be used to solve "deadly embrace" Feb 1, 2021

Extend API a bit

ce715df

rix0rrr removed the pr/do-not-merge This PR should not be merged at this time. label Feb 1, 2021

Merge branch 'master' into huijbers/deadly-embrace

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mergify bot merged commit 3b66088 into master Feb 1, 2021

mergify bot deleted the huijbers/deadly-embrace branch February 1, 2021 14:17

henrist reviewed Feb 1, 2021

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ghost mentioned this pull request Feb 1, 2021

Document using stack.ExportValue() to avoid "deadly embrace" awsdocs/aws-cdk-guide#296

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BenChaimberg mentioned this pull request Feb 5, 2021

Dependency stacks cause update failure #3414

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juanqui mentioned this pull request Feb 12, 2021

(core): stack.exportValue() does not work with ref parameters #13002

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mmmeff mentioned this pull request Mar 3, 2021

ReactCDK: Add JSX/TSX Support aws/aws-cdk-rfcs#256

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njlynch mentioned this pull request Mar 19, 2021

@aws-cdk/aws-cloudfront: Unable to deploy with EdgeFunction #13644

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eladb mentioned this pull request Apr 1, 2021

[core] Removing implicit references breaks deployment #9672

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corrjo mentioned this pull request Apr 14, 2021

feat(core): use parameter store refs instead of exports #13804

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ansgarm mentioned this pull request Jan 10, 2022

feat(lib): cross-stack references hashicorp/terraform-cdk#1416

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feat(core): `stack.exportValue()` can be used to solve "deadly embrace" #12778

feat(core): `stack.exportValue()` can be used to solve "deadly embrace" #12778

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henrist Feb 1, 2021

		@@ -92,6 +92,36 @@ nested stack and referenced using `Fn::GetAtt "Outputs.Xxx"` from the parent.

		Nested stacks also support the use of Docker image and file assets.

		### Breaking automatic references

feat(core): stack.exportValue() can be used to solve "deadly embrace" #12778

feat(core): stack.exportValue() can be used to solve "deadly embrace" #12778

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feat(core): `stack.exportValue()` can be used to solve "deadly embrace" #12778

feat(core): `stack.exportValue()` can be used to solve "deadly embrace" #12778

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