| Region Support | Single region | Single region | Multiple regions | Multiple regions (up to 5) |
| Write Capability | Single writer (primary instance) | Multiple writers (can write to any instance) | Single writer (primary region only) | Single writer (primary region only) |
| Replication Type | Synchronous replication across AZs in the same region | Synchronous replication between multiple writer instances in the same region | Asynchronous replication between primary and read replicas in different regions | Asynchronous physical replication between regions |
| Replication Lag | No replication lag between AZs (synchronous) | Minimal lag (synchronous) | Higher lag (asynchronous) | Minimal lag (<1 second) between regions |
| Disaster Recovery | Automatic failover to standby instance in the same region | Automatic failover between writers within the same region | Manual promotion of read replica to primary, higher downtime | Fast failover to secondary region within ~1 minute |
| Global Reads | No (only within the region) | No (only within the region) | Yes (replica in other region can serve read requests) | Yes (low-latency global reads with replicas in multiple regions) |
| Scalability | Limited to the primary instance and read replicas | Horizontal scalability within the same region with multiple writers | Read scalability across multiple regions with replicas | Read scalability across multiple regions with up to 15 replicas per region |
| Cost | Standard RDS pricing (one primary and one standby instance) | Higher costs due to multiple writer instances in the same region | Costs for data transfer, replication, and cross-region storage | Higher costs due to cross-region replication and storage, but cost-effective compared to cross-region read replicas |
| Write Conflict Handling | Not applicable (one primary writer) | Handles write conflicts using Aurora’s distributed architecture | Not applicable (single primary writer) | Not applicable (single primary writer) |
| Backup and Storage | Synchronous backups across AZs | Synchronous backups across writer instances | Backup in the primary region, replica region is read-only | Continuous backups to S3, replicated across regions |
| Use Case | Highly available single-region applications, failover within the same region | Write-heavy applications with multiple writers in the same region | Low-latency reads for globally distributed applications | Global applications requiring low-latency reads and fast disaster recovery |
