This image shows an Oracle Cloud region within a single VCN, a regional subnet, and a single availability domain with three fault domains, each with a PostgreSQL instance:

Data flows from the Customer Data Center using IPSec VPN / Oracle Cloud Infrastructure FastConnect through a DRG to the PostgreSQL (Master). Data flows from the internet through the Bastion Service to the PostgreSQL (Master), PostgreSQL (Hot standby 1), and PostgreSQL (Hot standby 2). WAL record flows from the PostgreSQL Master to each of the other postgreSQL instances (Hot standby 1 and Hot standby 2).

The VCN has a NAT Gateway and a DRG Gateway. A security list resides withing the regional subnet. Route tables located in the VCN and are used to direct traffic from the subnet to the appropriate destination outside the VCN.