GCP Professional Cloud Architect Practice Question

An online ticketing company runs its payment API on Compute Engine managed instance groups (MIGs) in the us-central1 region behind an external HTTP(S) load balancer. Orders are stored in a regional Cloud SQL for MySQL instance that uses standard (single-primary) configuration. Management mandates that if the entire us-central1 region becomes unavailable, payment processing must resume within 30 minutes and lose at most 5 minutes of data, while incurring the lowest additional cost that still meets these objectives. Which disaster-recovery design should you recommend?

Migrate the database to a multi-region Cloud Spanner instance for zero RPO and keep the application deployed only in us-central1 to minimize compute costs.
Create a cross-region read replica of Cloud SQL in us-east1, automate replica promotion on failure, and deploy an equivalent MIG in us-east1 as a failover backend of the same global HTTP(S) load balancer.
Schedule nightly Cloud SQL exports to Cloud Storage, replicate the export bucket to us-east1, and prepare Deployment Manager templates to recreate the database and VMs on demand after an outage.
Enable Cloud SQL high-availability (regional) configuration and add a second zonal MIG in another zone of us-central1 behind an internal TCP/UDP load balancer.

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Answer Description

Creating a cross-region read replica of the Cloud SQL primary in another region keeps the replica asynchronously updated, and typical replication lag is seconds-well inside the 5-minute RPO. Promoting the replica to primary during a regional outage is a documented procedure that can be automated to finish in minutes, satisfying the 30-minute RTO. Deploying a second MIG in the same target region and adding it as a failover backend to the global external HTTP(S) load balancer lets traffic switch automatically when the original region is unreachable, with minimal incremental cost (only the replica instance and additional autoscaled VMs).

Enabling only regional HA for Cloud SQL or placing all resources in one region cannot survive a full-region failure. Relying on nightly exports and manual recreation would exceed both the 5-minute RPO and 30-minute RTO. Migrating to Cloud Spanner multi-region would meet the objectives but at a significantly higher ongoing cost than a single Cloud SQL primary plus one read replica, so it is not the lowest-cost solution that satisfies the requirements.

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