The image shows an Oracle Cloud Infrastructure region containing a single availability domain (AD). This AD contains three fault domains (FD), numbered 1, 2, and 3. The region also contains a virtual cloud network (VCN) that spans the AD and all three FDs. Access to this VCN is through an Internet gateway. The VCN is divided into four subnets, tow public and two private. Access to each subnet is controlled by a routing table and a security list.

Traffic into the VCN through the Internet gateway is directed either to a bastion host in FD2 of the first pubic subnet, to either an active load balancer in FD1 or a standby load balancer in FD2, both in the second public subnet. From the load balancers, traffic then is directed to one of two Ruby on Rails servers, one in FD1 or FD2 of the first private subnet. These servers communicate with each other and each directs traffic to a primary MySQL database in FD1. Redundant secondary MySQL databases are available in FD2 and FD3. Traffic can flow between all three of these databases, as necessary.