publiclyAccessible
Specifies whether the DB instance is publicly accessible.
When the DB instance is publicly accessible, its Domain Name System (DNS) endpoint resolves to the private IP address from within the DB instance's virtual private cloud (VPC). It resolves to the public IP address from outside of the DB instance's VPC. Access to the DB instance is ultimately controlled by the security group it uses. That public access is not permitted if the security group assigned to the DB instance doesn't permit it.
When the DB instance isn't publicly accessible, it is an internal DB instance with a DNS name that resolves to a private IP address.
For more information, see CreateDBInstance.