GCP Professional Cloud Architect Practice Question

You need to design the database layer for a global e-commerce platform being migrated to Google Cloud. The platform must process strongly consistent ACID transactions, sustain unpredictable spikes to tens of thousands of writes per second, and offer at least 99.999 percent availability to customers in North America and Asia without manual sharding or complex replica management. Which approach best satisfies the business requirements while minimizing operational overhead?

Deploy Cloud SQL for MySQL with regional high availability, create asynchronous cross-region read replicas, and redirect traffic through Cloud SQL Auth Proxy during failover.
Provision a multi-region Cloud Spanner instance (for example, nam-asia3) and connect stateless services deployed in multiple regions to it.
Store transactional data in Firestore in Datastore mode with a multi-region configuration and rely on eventual consistency outside entity groups for global access.
Use Cloud Bigtable clusters in two regions with application-level row-timestamp conflict resolution and custom sharding logic.

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Answer Description

A multi-region Cloud Spanner instance is specifically engineered for globally distributed, strongly consistent relational data. It delivers a 99.999 % availability SLA in multi-region configurations, provides automatic horizontal scaling for high write throughput, and removes the need for application-level sharding or replica orchestration.

Cloud SQL's regional HA plus cross-region replicas offers only a 99.95 % SLA and uses asynchronous replication, so it cannot guarantee the required availability or global strong consistency. Cloud Bigtable can scale writes but is not ACID and becomes eventually consistent when using multi-cluster routing, requiring custom conflict resolution. Firestore in Datastore mode provides ACID semantics only within entity groups and falls back to eventual consistency for cross-group transactions, making it unsuitable for the strict consistency requirement.

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