An enterprise hosts a mission-critical database on a Cloud SQL instance configured for high availability (HA) within a single Google Cloud region. The organization wants to expand its disaster recovery (DR) architecture to protect against a potential full regional outage and achieve a recovery time objective (RTO) measured in minutes. Which replication strategy should the enterprise implement?

Configure an asynchronous cross-region read replica in a secondary region that can be promoted to primary if the primary region becomes unavailable.: ### **What cross-region read replicas in Cloud SQL are:** A **cross-region read replica** is a separate Cloud SQL instance provisioned in a different geographic region from the primary database instance. It continuously synchronizes data from the primary instance using **asynchronous replication**. In disaster recovery (DR) planning, cross-region replicas provide geographic redundancy across independent failure domains. ### **How it meets the disaster recovery requirements:** - **Regional disaster mitigation (✓):** Because the replica resides in a physically separated secondary region, a catastrophic failure or full outage of the primary region does not affect the replica's availability. - **Rapid failover and low RTO (✓):** If the primary region fails, database administrators or automated workflows can immediately **promote the cross-region read replica** to become the new standalone primary database instance, achieving a Recovery Time Objective (**RTO**) in minutes. - **Continuous synchronization (✓):** Ongoing transactional updates are replicated across regions without requiring manual data dumps or heavy export/import steps. ### **Key advantages and capabilities:** - **Read scalability:** Serves read queries locally in secondary regions during normal operations to reduce application latency. - **Predictable recovery path:** Promotion converts an existing, populated database instance directly into a read-write primary. - **Cascadable architecture:** Supports cascading read replicas attached to the cross-region replica to optimize cross-region network transfer costs. - **Supports fallback strategies:** Facilitates establishing reverse replication and fallback to the original region once service is restored. ### **Why this is optimal:** Standard Cloud SQL High Availability (HA) protects only against **zonal failures** within a single region. When business continuity demands protection against an entire regional outage with short RTO/RPO targets, configuring and promoting a **cross-region read replica** is Google Cloud's recommended architecture. Alternative approaches, such as restoring from backups or re-importing data dumps, require significant time to provision storage and replay files, resulting in hours of downtime instead of minutes.