This image shows an Oracle Cloud Infrastructure (OCI) region with 2 availability domains, 3 fault domains, and 1 virtual cloud network (VCN).

The region provides the following services:

Oracle Analytics Cloud (OAC)
Oracle Cloud Guard
Oracle Cloud Infrastructure Functions
Oracle Cloud Infrastructure Identity and Access Management
Oracle Cloud Infrastructure Notifications
Oracle Cloud Infrastructure Object Storage
Oracle Cloud Infrastructure Web Application Firewall (WAF)

The VCN provides the following gateways:

Internet gateway: Provides communications between public subnets and internet hosts.
Network address translation (NAT) gateway: Enables private resources in a VCN to access hosts on the internet, without exposing those resources to incoming internet connections.
Dynamic routing gateway (DRG): Provides private connectivity between on-premises networks and VCNs by using Site-to-Site VPN or FastConnect.
Service gateway: VCNs communicate with services such as object storage over the Oracle network fabric without traversing the internet.

Business users access the region by using an external domain name service (DNS). The OCI WAF passes incoming traffic to OCI application programming interfaces (APIs) and then to a Mainframe Load Balancer public subnet that manages traffic to subnets in the 2 availability domains.

The VCN also provides the following 3 subnets in the active availability domain (1) paired with 3 similarly configured subnets in the standby availability domain (2) :

Mainframe Frontend private subnet: Provides compute instances with mainframe frontend app servers in each of 3 fault domains.
Mainframe Backend private subnet: Provides compute instances with customer information control system (CICS) and information management system (IMS) modules in each of 3 fault domains.
Mainframe Database private subnet: Provides and instance of Oracle Exadata Database Service on Dedicated Infrastructure. The active and standby instances are synchronized by using Oracle Data Guard.