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Google ACE Practice Question: Set up a cost-effective disaster recovery…
A company wants to set up a cost-effective disaster recovery solution for a critical application running on Compute Engine. The primary region is us-east1. The recovery point objective (RPO) is 1 hour, and recovery time objective (RTO) is 4 hours. Which strategy is most cost-effective?
⚠ Common exam trap
Google Cloud often tests the misconception that active-active or multi-region instance groups are always the best for disaster recovery, but the trap here is that for cost-effectiveness with moderate RPO/RTO, a snapshot-based replication strategy is more appropriate than maintaining always-on infrastructure.
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
✓
Cross-region replica of persistent disks using snapshot schedules every hour
The most cost-effective because it uses snapshot schedules to create cross-region replicas of persistent disks every hour, meeting the 1-hour RPO without requiring always-on compute resources. This approach minimizes costs by only storing incremental snapshots in Cloud Storage, while automated restore procedures can spin up instances in the secondary region within the 4-hour RTO.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Regular backups to Cloud Storage with automated scripts to restore in a different region
Why it's wrong here
While Cloud Storage offers durable object storage, this approach requires custom scripting for disk export, validation, and cross-region transfer, adding operational complexity and potential for restore failure. Snapshots natively integrate with Compute Engine, create incremental crash-consistent captures automatically, and can be promoted to disks in another region more reliably than assembling a disk from stored files, making this less integrated and slower for DR.
- ✗
Use managed instance groups in two regions with autoscaling
Why it's wrong here
Running MIGs in two regions keeps live compute resources in both locations, incurring continuous costs for idle or lightly utilized instances, which is wasteful for disaster recovery. Autoscaling responds to load, not to failover or data replication; without pre-provisioned replicated disks, starting an instance template does not restore state quickly and can exceed RTO. This approach also neglects persistent data restoration, a core requirement of DR.
- ✓
Cross-region replica of persistent disks using snapshot schedules every hour
Why this is correct
Snapshot schedules automatically take incremental persistent disk snapshots at defined intervals, providing a predictable hourly RPO while minimizing storage costs because only changed blocks are captured. These snapshots are a native Compute Engine feature and can be used to create new disks in a target region during failover, streamlining replication and restoration without custom code. This balance of cost, integration, and recoverability makes it the most practical, cost-effective DR choice.
- ✗
Active-active multi-region deployment with HTTP load balancer
Why it's wrong here
An active-active deployment requires running full production stacks in multiple regions simultaneously with synchronous or near-real-time data replication, which doubles infrastructure and licensing costs and introduces complex conflict-resolution requirements. The HTTP load balancer only routes traffic and does not replicate persistent state, so it fails to provide DR for stateful applications without additional storage mirroring or database replication. For cost-effective DR, an active-passive setup with snapshots or replicated disks is sufficient, avoiding always-on secondary region costs.
Go deeper
Related to this question
Learn chapter
Google Cloud Platform Overview
Key term
Region
A region is a distinct geographic location where a cloud provider operates multiple data centers that are connected by low-latency networks and provide cloud services.
Key term
Cloud storage
Cloud storage is a service that lets you save data on remote servers accessed over the internet instead of on your computer's hard drive.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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