This image shows a multitier application topology deployed in an Oracle Cloud Infrastructure tenancy, with the resources in each tier replicated across two regions: the primary region, US West (Phoenix) and the standby region, US East (Phoenix).

The resources in each region are attached to a single VCN. The VCNs in the two regions are peered remotely using dynamic routing gateways (DRGs) at either end.

Requests from users outside the cloud are forwarded by the DNS service to the internet gateway of the appropriate region: primary or standby. Application traffic is received by a public load balancer. Administrative access to the topology is controlled through a bastion host in a public subnet.

The load balancer distributes requests to the application servers in a private subnet.

The compute instances that host the application have access to block storage and also shared file storage.

The application tier has connectivity to a database that's in a separate private subnet. The primary database is replicated to a database in the standby region using Active Data Guard.

A NAT gateway attached to each VCN enables access from the resources in the private subnets to the internet.

A service gateway attached to each VCN enables connectivity to Oracle Cloud Infrastructure Object Storage.