You have three VPCs with one Compute Engine instance in each; subnets are non‑overlapping and must remain separate. Instance #1 must communicate directly with Instance #2 and Instance #3 via internal IPs. How do you accomplish this?

The correct answer is to add two additional NICs to Instance 1. This is the most direct and efficient solution because a single Compute Engine instance can have multiple network interfaces (NICs), each connected to a different VPC network. By attaching NICs connected to VPC 2 and VPC 3 directly to Instance 1, it gains direct internal IP connectivity to instances within those VPCs. Firewall rules must be updated to permit the traffic. Creating a Cloud Router is incorrect because Cloud Router is used for dynamic routing with VPNs or Interconnects, not for direct instance-to-instance communication across separate VPCs in this manner. Creating two VPN tunnels is incorrect because VPNs are typically used for secure connections over the internet or between on-premises networks and GCP, adding unnecessary overhead and complexity for intra-GCP communication. Peering all three VPCs is incorrect because VPC Network Peering allows two VPC networks to communicate using internal IP addresses, but it doesn't allow a single instance in one VPC to directly access instances in other peered VPCs via their internal IPs without additional routing or network interface configurations on the instance itself.