This option controls how the Amazon EC2 plugin connects to the Amazon EC2 instance. It is only applicable if the instance belongs to a VPC (and thus it has a Private IP address) and it has been configured to have a Public IP address (using the Associate Public IP option above). The default plugin behavior in this case is to connect to the instance using its Private IP; enabling this option will modify that behavior, and the plugin will connect to the instance using its Public IP address.