Ref resource from another CloudFormation without output?

Question

Is it a way to reference a resource of another CloudFormation which is not outputted?

For example, in file1.yaml

Resource:
  SG1:
    Type: AWS::EC2::SecurityGroup
    ....

And in file2.yaml, I will need to reference SG1

  SGMSKClusterIgress6:
    Type: AWS::EC2::SecurityGroupIngress
    Properties:
      SourceSecurityGroupId: SG1 # How to reference SG1 here
      GroupId: !ImportValue MySecurityGroup
      IpProtocol: tcp
      FromPort: 443
      ToPort: 443

I know if there is Outputs in the file1.yaml, for example,

Resource:
  SG1:
    Type: AWS::EC2::SecurityGroup
    ....
Outputs:
  SG1Output:
    Value: !Ref SG1
    Export:
      Name: File1SG1

I can use it in file2.yaml as

      SourceSecurityGroupId: !ImportValue File1SG1 # SG1 output name

What if it's not outputted? Do I has to modify file1.yaml to add the Outputs section and update the provisioned product?

Answer 1

Yes for referencing resources in terms of CloudFormation, you should use outputs. In case that you don't have access to file1.yaml, you can create a parameter in file2.yaml where you specify security group id and reference it in resource creation