Explanation/Reference: https://docs.cloud.oracle.com/en-us/iaas/Content/Tagging/Tasks/ managingaccesswithtags.htm#about

https://docs.cloud.oracle.com/iaas/Content/GSG/Tasks/loadbalancing.htm#Create Enter the Health Check details.
Load Balancing automatically checks the health of the instances for your load balancer. If it detects an unhealthy instance, it stops sending traffic to the instance and reroutes traffic to healthy instances. In this step, you provide the information required to check the health of servers in the backend set and ensure that they can receive data traffic.
Protocol: Select HTTP. Port: Enter 80 URL Path (URI): Enter / The rest of the fields are optional and can be left blank for this tutorial.
Click Create.

Reference:
https://docs.cloud.oracle.com/en-us/iaas/Content/Object/Tasks/usingretentionrules.htm

Explanation
You can think of a DRG as a virtual router that provides a path for private traffic (that is, traffic that uses private IPv4 addresses) between your VCN and networks outside the VCN's region.
You use a DRG when connecting your existing on-premises network to your virtual cloud network (VCN) with one (or both) of these:
IPSec VPN
Oracle Cloud Infrastructure FastConnect (Private Only)
You also use a DRG when peering a VCN with a VCN in a different region:
Remote VCN Peering (Across Regions)