CODEWITHSUNDEEP
aws-cloudformation
Justin
Justin

Reputation: 4853

Cloudformation nested stack import/export - No export named EXPORT_NAME found

I have a Cloudformation stack with a master template and two nested templates, one of which contains a Lambda and associated role, another which contains an S3 bucket. I want to export the Lambda ARN from the Lambda template and pass it to the S3 template so I can do some event notification stuff (have a new item in the S3 bucket trigger the Lambda).

If I comment out the CF code in the master template which imports the exported Lambda ARN and passes it to the bucket, everything works fine - the master and nested templates deploy fine, and I can see the exported Lambda ARN -

(c4abb639548f2545e145ea54ed13d2ea) justin@justin-XPS-13-9360:~/work/gists/c4abb639548f2545e145ea54ed13d2ea$ ./describe_outputs.sh xxx-MyLambda-1B451J61821EC
------------------------------------------------------------------------------------------------------------------
|                                                 DescribeStacks                                                 |
+-------------------------+--------------+-----------------------------------------------------------------------+
|       ExportName        |  OutputKey   |                              OutputValue                              |
+-------------------------+--------------+-----------------------------------------------------------------------+
|  xxx-lambda-arn|  FunctionArn |  arn:aws:lambda:eu-west-1:119552584133:function:xxx-lambda   |
+-------------------------+--------------+-----------------------------------------------------------------------+

However if I uncomment the code passing the exported Lambda ARN to the bucket template -

  MyBucket:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: !Sub "https://s3.${AWS::Region}.amazonaws.com/${S3Bucket}/${AppName}/templates/bucket.yaml"
      Parameters:
        BucketName: !Join
          - '-'
          - - Ref: AppName
            - bucket
        LambdaArn:                            # <- this
          Fn::ImportValue:                    # <- this
            Fn::Sub: "${AppName}-lambda-arn"  # <- this

then suddenly deployment of the entire stacks fails -

(c4abb639548f2545e145ea54ed13d2ea) justin@justin-XPS-13-9360:~/work/gists/c4abb639548f2545e145ea54ed13d2ea$ aws cloudformation describe-stack-events --stack-name xxx
{...}
ROLLBACK_IN_PROGRESS |  No export named xxx-lambda-arn found. Rollback requested by user.

I'm surprised the main stack isn't able to detect that one of its nested stacks (the S3 stack) needs a value to be exported from the other nested stack (the Lambda stack).

I hoped this might be resolvable by adding a DependsOn block, making the S3 nested stack dependent on the Lambda nested stack, but this doesn't work either.

Is there some kind of restriction on importing/exporting values across nested stack belonging to the same master stack ? Or is there a workaround ?

Full gist here -

https://gist.github.com/jhw/c4abb639548f2545e145ea54ed13d2ea

Upvotes: 4

Views: 15475

Answers (1)

David Webster
David Webster

Reputation: 2321

In your nested stack, you need to specify an output so the master stack has access to it from the resource i.e.

Lambda Stack

"Resources": {
    "LambdaFunction": ...
}
"Outputs": {
    "LambdaFunction": {
                "Value":
                { "Fn::GetAtt": ["LambdaFunction","Arn"] }
    }

Master Stack

LambdaArn: !GetAtt Lambda.Outputs.LambdaArn

The Lambda can be referenced from the master stack for more information take a look at this reference architecture https://github.com/aws-samples/ecs-refarch-cloudformation.

Upvotes: 5

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