PCNE Inter-region latency Practice Question
Your company runs a multi-tier web application on Google Cloud. The application consists of frontend instances in a managed instance group (MIG) in us-central1, backend instances in a MIG in us-west1, and a Cloud SQL database in us-central1. The frontend and backend communicate over a VPC network with custom subnet mode (10.0.0.0/16) and use internal IP addresses. Recently, the application experienced intermittent timeouts. You notice that the backend instances in us-west1 have high latency when querying the Cloud SQL database in us-central1. You suspect network congestion or suboptimal routing. You want to minimize latency between the regions for database queries while ensuring the most cost-effective solution. What should you do?
⚠ Common exam trap
Google Cloud often tests the misconception that Cloud VPN with BGP can optimize routing within the same VPC, but the trap here is that VPN is for connecting separate networks, not for enhancing internal routing. The real solution is consolidation to a single region.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Move all resources to a single region, such as us-central1, and use a single VPC.
The latency issue stems from inter-region communication between the backend and Cloud SQL database. By moving all resources to a single region (us-central1), you eliminate cross-region traffic entirely, reducing latency to the minimum possible within that region. This is the most cost-effective solution as it avoids any additional networking costs and simplifies the architecture. While it may require a redesign of the MIGs, it directly addresses the root cause of high latency. Option B (Cloud VPN) adds a VPN tunnel over the Google backbone, which would introduce extra latency and cost without solving the underlying routing issue within the same VPC. Option C (VPC peering) is irrelevant since the resources are already in the same VPC. Option D (Cloud CDN) is designed for caching static content, not database queries, and would not reduce latency for dynamic database traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Move all resources to a single region, such as us-central1, and use a single VPC.
Why this is correct
Correct. Consolidating all resources to a single region eliminates cross-region latency, reducing database query times and simplifying the network.
- ✗
Set up a Cloud VPN tunnel with Cloud Router and use BGP to advertise routes between the two regions.
Why it's wrong here
Incorrect. Cloud VPN with BGP is designed for hybrid cloud or multi-network connectivity, not for optimizing routing within the same VPC. It adds latency and cost without benefit.
- ✗
Create a VPC peering connection between the frontend and backend VPCs.
Why it's wrong here
Incorrect. VPC peering connects separate VPC networks; the frontend and backend are already in the same VPC, so peering provides no advantage.
- ✗
Enable Cloud CDN on the backend load balancer to cache database responses.
Why it's wrong here
Incorrect. Cloud CDN caches static content from HTTP(S) load balancers; it cannot cache database responses or reduce latency for dynamic queries.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNE exam.