Your team needs to make sure that their backend database can only be accessed by the frontend application and no other instances on the network. How should your team design this network?

Creating an ingress firewall rule allows precise control over network traffic, enabling the configuration to permit access to the database only from specific sources, such as the frontend application instances (e.g., via IP addresses, network tags, or service accounts), and block all other traffic.

Creating different subnets provides network segmentation but does not, by itself, restrict traffic between instances in those subnets within the same VPC; explicit firewall rules are still required for granular access control.

Using two separate VPC networks connected by Cloud VPN is an overly complex and expensive solution for securing communication between a frontend and backend application that are logically part of the same environment and would still require internal firewall rules for specific access control.

Connecting two VPC networks via VPC peering makes them appear as one for routing purposes, but it does not inherently provide the granular access control needed to restrict database access solely to the frontend application without additional firewall rules.