ElastiCache Global Datastore (Valkey) Multi-Region Architecture Diagram

One Primary, Read-Only Replicas

Writes land on the US primary; replica regions serve local reads
The replica rejects writes until promoted, so there is never a split-brain write path

Measured Stale-Read Window

Acceptance prints the replication visibility delay in milliseconds
Asynchronous replication is the RPO contract: unreplicated writes can be lost on promotion

Promotion Failover

Router steers traffic to the surviving region during a full primary outage
The old primary rejoins as a replica of the promoted region and converges

📍 Case 1: Aurora HA (Single Writer)⚡ Case 2: Cassandra (Active-Active)🔄 HTTP Sync vs Queue Async Flows 🧠 Case 3: ElastiCache Global (Valkey)