You need production and test VMs on Compute Engine in different subnets but reachable to each other via Internal IP without extra routes. How should you configure VPC and subnets?

The correct approach is to create a single custom VPC with two subnets, each in a different region and with different CIDR ranges. A single VPC allows all subnets within it to communicate via internal IP addresses without requiring additional routing configurations like VPC peering or VPNs, as long as the CIDR ranges do not overlap. Placing subnets in different regions provides geographical distribution and fault tolerance. Using different CIDR ranges is crucial to prevent IP address conflicts. Incorrect options: "Single custom VPC with two subnets in the same region using the same CIDR range" is incorrect because subnets within the same VPC cannot have overlapping CIDR ranges. "Two custom VPCs each with one subnet" (both same and different regions/CIDRs) is incorrect because VMs in different VPCs cannot communicate via internal IP addresses without explicit peering or VPN connections, which the question states should be avoided.