This image shows an Oracle Cloud Infrastructure (OCI) region and a second, disaster recovery region. Each region has 1 availability domain, 3 fault domains, and 1 virtual cloud network (VCN).

The primary 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 in each region 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.

The VCN in the primary region provides the following additional gateways:

• 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 subnets in the region. Each region provides similarly configured VCN subnets:

• Mainframe Load Balancer public subnet: Manages traffic to the subnets in the VCN.
• Mainframe Frontend private subnet: Provides compute instances with mainframe frontend app servers in each of 3 fault domains. Instances in the primary and standby regions are synchronized by using rsync.
• 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. Instances in the primary and standby regions are synchronized by using rsync.
• 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.