3.1.1.7. Enabling Cross-Region Solutions (DynamoDB, RDS, Route 53, S3, CloudFront)
3.1.1.7. Enabling Cross-Region Solutions (DynamoDB, RDS, Route 53, S3)
Cross-region architectures protect against regional outages and serve users globally with lower latency. Each service has a different mechanism for cross-region data synchronization.
DynamoDB Global Tables: Active-active replication across up to 5 regions. Writes in any region propagate automatically (typically < 1 second). Conflict resolution: last-writer-wins based on timestamp. No application changes needed — reads and writes work against the local table.
RDS Cross-Region Read Replicas: Asynchronous replication to another region. The replica is read-only; you must manually promote it to a standalone instance during failover (RPO > 0 due to replication lag). Aurora Global Database provides faster replication (< 1 second lag) with managed failover.
Route 53 cross-region routing:
- Failover routing: Primary region serves traffic; Route 53 health check detects failure and routes to secondary
- Latency-based routing: Routes users to the lowest-latency region automatically
- Geolocation routing: Routes based on user's geographic location (compliance use case)
S3 Cross-Region Replication (CRR): Asynchronous object replication between buckets in different regions. Requires versioning enabled on both buckets. Replicates new objects; existing objects need a one-time batch replication job.
Exam Trap: S3 CRR only replicates new objects created after the rule is enabled. Existing objects must be copied using S3 Batch Operations or aws s3 sync. If a DR question says "all existing data must be available in the secondary region," CRR alone is insufficient — you need the initial sync first.
