GCP Networking Interview Questions: VPC and Load Balancing Scenarios

Engineers walking into a GCP networking interview from an AWS or Azure background usually know the product names before the interview starts — VPC, Cloud Load Balancing, Cloud NAT — and that familiarity can be a trap. GCP's networking model is structurally different from AWS and Azure in a couple of specific places, and interviewers who work with GCP daily will notice within one question whether a candidate actually understands the difference or is just pattern-matching from another cloud.

The One Fact That Changes Every Other Answer: VPC Is Global

In AWS and Azure, a VPC or VNet is a regional resource — you create one per region and connect them with peering, a transit gateway, or a virtual WAN. In GCP, a VPC network is a global resource, and subnets are the regional pieces attached to it. Practically, that means an instance in a us-central1 subnet and an instance in a europe-west1 subnet can belong to the same VPC network, communicate over Google's private backbone by default, and never need a peering connection or transit device between them, because they were never in separate networks to begin with. This is the single fact most likely to surface as a scenario question — "why doesn't this GCP design need a Transit Gateway equivalent between these two regions" — and candidates who answer with a peering explanation instead of naming the global-VPC model give away that their GCP knowledge is shallow.

Shared VPC: Centralizing the Network Without Centralizing the Org

Shared VPC is GCP's answer to a very real organizational problem: how do you let a platform or network team own firewall rules, routes, and subnet design for an entire company, while individual product teams still own their own compute, storage, and IAM inside their own projects? A host project owns the VPC network; service projects are attached to it and granted access to specific subnets through IAM roles like Network User, without ever touching the host project's own resources. If an interviewer describes a company with forty engineering teams and asks how you'd stop network sprawl without becoming a bottleneck that approves every VM's networking, Shared VPC is the architecture they're listening for.

VPC Peering vs. Private Service Connect: Two Different Jobs

These two get confused constantly, and the confusion is the interview question. VPC Peering connects two full VPC networks to each other over internal IPs — it's symmetric, and like AWS peering, it is non-transitive, meaning a network peered to yours cannot forward traffic on to a third network peered to it. Private Service Connect solves a narrower, more common problem: exposing one specific service from a producer VPC to a consumer VPC as a single internal IP address, with traffic flowing one direction only. If the scenario is "two teams' networks need full bidirectional reachability," that's peering. If the scenario is "a platform team needs to publish an internal API to dozens of consumer projects without handing out full network access to any of them," that's Private Service Connect — the same shape of problem AWS PrivateLink solves, just under a different name.

Load Balancing: Global Reach, Regional Reality

GCP's load balancer family splits along the same global-versus-regional line as VPC itself. A global external Application Load Balancer uses Google's front-end anycast layer, so a single IP address can serve users on every continent and route each request to the closest healthy backend — no DNS-based geo-routing required to get that behavior. Regional external and internal Application Load Balancers, by contrast, run on Envoy proxies that need somewhere to live: a dedicated proxy-only subnet in each region, reserved specifically for that purpose and never used for VM workloads. Forgetting to provision that subnet is a genuinely common deployment failure, and naming it unprompted is one of the fastest ways to signal you've actually deployed one of these, not just read the architecture diagram.

The Troubleshooting Scenario Interviewers Actually Ask

A frequent live scenario: "users in one region are getting intermittent 502s from your global load balancer, other regions are fine — walk me through it." The disciplined path is backend health checks first (is the regional backend group actually marked healthy), then capacity and balancing mode (RATE versus UTILIZATION, and whether that region's backends are simply saturated), then the regional proxy-only subnet itself (is it exhausted of IPs, which silently caps how many Envoy proxies can run there), and only after those are ruled out do you move into application-layer debugging. The candidates who jump straight to application logs usually haven't operated a GCP load balancer under real traffic.

None of this replaces reading GCP's own architecture documentation, but interviews rarely test whether you've read the docs — they test whether you can apply the model to a scenario you haven't seen phrased exactly that way before. My Next Hop's Free Drill and Custom Question modes let you throw a specific GCP scenario — a Shared VPC design question, a load balancer failing over in one region, a Private Service Connect exposure decision — at an AI interviewer that scores the reasoning, not just whether you named the right product.