The image shows a disaster recovery architecture that uses two OCI regions, a primary and secondary.

Each region has a VCN with an Internet Gateway, a Dynamic Routing Gateway (DRG), a DR protection group, and the following subnets:

Public subnet contains a load balancer.
Private subnet contains a Virtual Machine (VM), boot volume and block volume, and OCI File Storage. Data flows from the VM to the boot volume and block volume. Data flows bi-directionally between the VM and OCI File Storage.
Private subnet contains the database.

A DNS or local resolution and client are outside of Oracle Cloud Infrastructure. The DNS has two-way communication with the Client and the client sends information to the Internet and to OCI through an Internet Gateway on the VCN.

For DR, two-way communication occurs between the regions for the following:

Cross region replication occurs between the boot volume and block volume in each region.
Cross region replication occurs between the boot volume and block volume in each region.
Remote peering occurs between DRG-1 on the primary and DRG-2 on the secondary.
Oracle Data Guard between the databases in each region.