Google PCA Manage implementation of cloud architecture Practice Question
A company is using Cloud Load Balancing to distribute traffic to a managed instance group (MIG) of web servers. The web servers are currently running in us-central1. To improve availability, the company plans to add a second MIG in us-west1. What must be done to ensure traffic is automatically routed to the closest healthy backend?
⚠ Common exam trap
A common mix-up: candidates confuse regional load balancers (Network Load Balancer, TCP/UDP Proxy) with global load balancers, assuming any external load balancer can span regions, but only the global external HTTP(S) load balancer (and the global external SSL proxy) support multi-region backends with automatic proximity-based routing.
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
✓
Use a global external HTTP(S) load balancer and add both MIGs as backends.
A global external HTTP(S) load balancer can route traffic to backends in multiple regions and automatically directs requests to the closest healthy backend based on the client's geographic location and backend health. Adding both MIGs as backends to this single anycast IP ensures traffic is distributed to the nearest region without additional DNS-based routing or redirects.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a Network Load Balancer in us-central1 and configure a redirect to the new MIG.
Why it's wrong here
A Network Load Balancer is regional, so it cannot redirect to a MIG in us-west1; redirects also operate at the HTTP layer, which a TCP/UDP load balancer does not provide. Regional load balancers suit single-region TCP/UDP workloads, not cross-region proximity routing.
- ✓
Use a global external HTTP(S) load balancer and add both MIGs as backends.
Why this is correct
A global external HTTP(S) load balancer provides a single anycast VIP with Google's global frontend, so it can route each user to the closest healthy backend across both us-central1 and us-west1 MIGs. A regional load balancer cannot span regions.
- ✗
Use an internal TCP/UDP load balancer in each region and configure DNS-based routing.
Why it's wrong here
Internal TCP/UDP load balancers are regional and cannot span us-central1 and us-west1, so DNS routing would be needed to stitch regions together, adding latency and health-check gaps. A single global external Application Load Balancer with both MIGs as backends performs the closest-backend routing automatically.
- ✗
Use an external TCP/UDP Network Load Balancer with the new MIG as an additional backend.
Why it's wrong here
An external TCP/UDP Network Load Balancer is regional, so adding a us-west1 MIG as a backend is not possible; backends must sit in the load balancer's region. Network Load Balancers suit non-HTTP protocols and static IPs, but global proximity routing across regions requires a global external Application Load Balancer.
Go deeper
Related to this question
Learn chapter
Load Balancing and Autoscaling
Key term
Managed instance group
A managed instance group is a collection of identical virtual machine instances that are automatically managed as a single unit to ensure high availability and scalability.
Key term
Cloud Load Balancing
Cloud Load Balancing is the process of distributing incoming network traffic across multiple servers or resources in the cloud to ensure no single resource is overwhelmed, improving availability and reliability.
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