Share Values upstream in a nested cloudformation stack possible? - aws-cloudformation

Question

Is there some way to pass on Values form a child stack to a parent stack? All I found was to pass values down, but never up, that would unfortunately not correspond with my stack architecture. I could use cross-referencing with eXport/Import but would rather keep the nested stack if possible.

Answer 1

You can definitely gather outputed values from a child stack and use them in the parent stack.
For example:
# parent stack
AWSTemplateFormatVersion: 2010-09-09
Resources:
SomeChildStack:
Type: AWS::CloudFormation::Stack
Properties:
Parameters:
AWS CloudFormation Stack Parameters
TemplateURL: !Ref SomeTemplateUrl
SomeOtherResource:
Type: AWS::AnyOther::Resources
Properties:
SomeProperty: !Ref SomeChildStack.Outputs.MyOutput
And in SomeChildStack:
# The template used for SomeChildStack
AWSTemplateFormatVersion: 2010-09-09
Resources:
S3Bucket:
Type: AWS::S3::Bucket
Properties:
AccessControl: PublicRead
LoggingConfiguration:
DestinationBucketName: !Ref 'LoggingBucket'
LogFilePrefix: testing-logs
Outputs:
MyOutput:
Value: !Ref 'S3Bucket'
Description: Name of the sample Amazon S3 bucket.
The tricky thing to remember is adding the Outputs when referencing the AWS::CloudFormation::Stack.
Note that this will make SomeOtherResource depend on SomeChildStack, so SomeOtherResource won't be created until SomeChildStack has been created.

Answer 2

We had the same issue and the accepted answer (using !Ref) didn't work. CloudFormation wouldn't deploy the stack.
What did work for us is:
!GetAtt [NestedStack, Outputs.MyOutput]
Parent stack:
AWSTemplateFormatVersion: 2010-09-09
Resources:
NestedStack:
Type: AWS::CloudFormation::Stack
Properties:
TemplateURL: !Ref NestedStackTemplateUrl
ResourceInParentStack:
Type: AWS::AnyOther::Resources
Properties:
SomeProperty: !GetAtt [NestedStack, Outputs.MyOutput]
Nested stack:
AWSTemplateFormatVersion: 2010-09-09
Resources:
S3Bucket:
Type: AWS::S3::Bucket
Properties:
BucketName: 'MyBucketName'
...
Outputs:
MyOutput:
Value: !Ref S3Bucket
Description: Name of the sample Amazon S3 bucket.