!ImportValue in Serverless Framework not working - aws-cloudformation

Question

I'm attempting to export a DynamoDb StreamArn from a stack created in CloudFormation, then reference the export using !ImportValue in the serverless.yml.
But I'm getting this error message:
unknown tag !<!ImportValue> in "/codebuild/output/src/serverless.yml"
The cloudformation and serverless.yml are defined as below. Any help appreciated.
StackA.yml
AWSTemplateFormatVersion: 2010-09-09
Description: Resources for the registration site
Resources:
ClientTable:
Type: AWS::DynamoDB::Table
DeletionPolicy: Retain
Properties:
TableName: client
AttributeDefinitions:
- AttributeName: id
AttributeType: S
KeySchema:
- AttributeName: id
KeyType: HASH
ProvisionedThroughput:
ReadCapacityUnits: 2
WriteCapacityUnits: 2
StreamSpecification:
StreamViewType: NEW_AND_OLD_IMAGES
Outputs:
ClientTableStreamArn:
Description: The ARN for My ClientTable Stream
Value: !GetAtt ClientTable.StreamArn
Export:
Name: my-client-table-stream-arn
serverless.yml
service: my-service
frameworkVersion: ">=1.1.0 <2.0.0"
provider:
name: aws
runtime: nodejs6.10
iamRoleStatements:
- Effect: Allow
Action:
- dynamodb:DescribeStream
- dynamodb:GetRecords
- dynamodb:GetShardIterator
- dynamodb:ListStreams
- dynamodb:GetItem
- dynamodb:PutItem
Resource: arn:aws:dynamodb:*:*:table/client
functions:
foo:
handler: foo.main
events:
- stream:
type: dynamodb
arn: !ImportValue my-client-table-stream-arn
batchSize: 1

Answer 1

Solved by using ${cf:stackName.outputKey}

Answer 2

I struggled with this as well, and what did trick for me was:
functions:
foo:
handler: foo.main
events:
- stream:
type: dynamodb
arn:
!ImportValue my-client-table-stream-arn
batchSize: 1
Note, that intrinsic functions ImportValue is on a new line and indented, otherwise the whole event is ignored when cloudformation-template-update-stack.json is generated.

Answer 3

It appears that you're using the !ImportValue shorthand for CloudFormation YAML. My understanding is that when CloudFormation parses the YAML, and !ImportValue actually aliases Fn::ImportValue. According to the Serverless Function documentation, it appears that they should support the Fn::ImportValue form of imports.
Based on the documentation for Fn::ImportValue, you should be able to reference the your export like
- stream:
type: dynamodb
arn: {"Fn::ImportValue": "my-client-table-stream-arn"}
batchSize: 1
Hope that helps solve your issue.

Answer 4

I couldn't find it clearly documented anywhere but what seemed to resolve the issue for me is:
For the Variables which need to be exposed/exported in outputs, they must have an "Export" property with a "Name" sub-property:
In serverless.ts
resources: {
Resources: resources["Resources"],
Outputs: {
// For eventbus
EventBusName: {
Export: {
Name: "${self:service}-${self:provider.stage}-UNIQUE_EVENTBUS_NAME",
},
Value: {
Ref: "UNIQUE_EVENTBUS_NAME",
},
},
// For something like sqs, or anything else, would be the same
IDVerifyQueueARN: {
Export: {
Name: "${self:service}-${self:provider.stage}-UNIQUE_SQS_NAME",
},
Value: { "Fn::GetAtt": ["UNIQUE_SQS_NAME", "Arn"] },
}
},
}
Once this is deployed you can check if the exports are present by running in the terminal (using your associated aws credentials):
aws cloudformation list-exports
Then there should be a Name property in a list:
{
"ExportingStackId": "***",
"Name": "${self:service}-${self:provider.stage}-UNIQUE_EVENTBUS_NAME", <-- same as given above (but will be populated with your service and stage)
"Value": "***"
}
And then if the above is successful, you can reference it with "Fn::ImportValue" like so, e.g.:
"Resource": {
"Fn::ImportValue": "${self:service}-${self:provider.stage}-UNIQUE_EVENTBUS_NAME", <-- same as given above (but will be populated with your service and stage)
}