Reference lambda function Arn from another nested Stack - aws-lambda

Question

I have two sam applications one 'App1' having a lambda function and another one 'App2' that will consume its Arn to create a permission like the following:
App2 template:
Parameters:
LambdaFunctionArnFromApp1:
Type: String
Description: The shared value will be passed to this parameter by parent stack.
DACAdminsLoginPermission:
Type: AWS::Lambda::Permission
Properties:
Action: lambda:InvokeFunction
FunctionName: LambdaFunctionArnFromApp1
Principal: apigateway.amazonaws.com
SourceArn: !Sub arn:${AWS::Partition}:execute-api:${AWS::Region}:${AWS::AccountId}:${HttpWebServer}/*/*/digitalatcore/admins/login
App1 template:
LambdaFunctionArnFromApp1:
Type: AWS::Serverless::Function
Properties:
CodeUri: 'URL'
Runtime: nodejs12.x
Handler: app.handler
Outputs:
LambdaFunctionArnFromApp1:
Value: !GetAtt LambdaFunctionFromApp1.Arn
Export:
Name: LambdaFunctionArnFromApp1
When i try to deploy the full stack with sam i get the following error :
"*** was not successfully created: The following resource(s) failed to create: [DACAdminsLoginPermission]. ROLLBACK_IN_PROGRESS"
Can anyone please help me with this.
thank you.

Answer 1

Assuming both nested stacks have the same parent stack, you can pass the output from the App1 stack to the App2 stack like this:
App1Stack:
Type: AWS::CloudFormation::Stack
Properties:
TemplateURL: app1-template.yaml
App2Stack:
Type: AWS::CloudFormation::Stack
Properties:
TemplateURL: app2-template.yaml
Parameters:
LambdaFunctionArnFromApp1: !GetAtt App1Stack.Outputs.LambdaFunctionArnFromApp1
Another option could be to use the ImportValue intrinsic function in your App2 template to get the export that you defined in the App1 template: FunctionName: !ImportValue LambdaFunctionArnFromApp1