Explanation
health check A test to confirm the availability of backend servers. A health check can be a request or a connection attempt. Based on a time interval you specify, the load balancer applies the health check policy to continuously monitor backend servers. If a server fails the health check, the load balancer takes the server temporarily out of rotation. If the server subsequently passes the health check, the load balancer returns it to the rotation.
You configure your health check policy when you create a backend set. You can configure TCP-level or HTTP-level health checks for your backend servers.
- TCP-level health checks attempt to make a TCP connection with the backend servers and validate the response based on the connection status.
- HTTP-level health checks send requests to the backend servers at a specific URI and validate the response based on the status code or entity data (body) returned.
The service provides application-specific health check capabilities to help you increase availability and reduce your application maintenance window.

Explanation
References: B - Support for Oracle Cloud Infrastructure, other Cloud provider endpoints (AWS, Azure) and private assets, including Cloud, CDNs and Data CentersC - Customers may purchase Oracle Cloud Infrastructure Private Pool and Vanity Nameserver to have their Domain Names and Zones under a private IP pool with dedicated nameservers to segregate from those of other customers in order to reduce the risk of external issues affecting their websites.
https://www.oracle.com/cloud/networking/dns-faq.html

Explanation
you may optionally specify one or more security lists for the subnet to use (up to five). If you don't specify any, the subnet uses the cloud network's default security list. You can change which security list the subnet uses at any time.
https://docs.cloud.oracle.com/iaas/Content/Network/Tasks/managingVCNs.htm