code: func Sub(value string) string {
  	i := `{ "Fn::Sub" : "` + value + `" }`
  	return base64.StdEncoding.EncodeToString([]byte(i))
  }
docs: // NewSub substitutes variables in an input string with values that you specify. In your templates, you can use this function to construct commands or outputs that include values that aren't available until you create or update a stack.