Import and export in AWS CloudFormation

 
- ContainerName: !Sub "${AWS::StackName}"
  ContainerPort: 80
  TargetGroupArn: { "Fn::ImportValue" : { "Fn::Join" : [ "-", [ { "Ref" : "EnvironmentType" }, "leo-elb-elb-target-group"]] }}

If EnvironmentType is sandbox, we are importing sandbox-leo-elb-elb-target-group as TargetGroupArn

# part of codes from stack sandbox-leo-elb
# export a resource called leo-elb-elb-target-group
# click Outputs tab in AWS console for this stack. Also see Export Name: leo-elb-elb-target-group
Outputs:
  ELBTargetGroupHTTP:
    Description: The target group
    Value: !Ref ELBTargetGroup
    Export:
      Name: !Sub "${AWS::StackName}-elb-target-group"