Multi-Region Architecture: Active-Active, Failover, and Replication
Multi-region is a list of trade-offs, not a diagram. We compare active-passive and active-active designs on the mechanics that matter: where writes land, how replication propagates, what the failover actually flips, and what RTO and RPO numbers really cost. We work through DNS-based failover, routing policies, cross-region replication of databases and object storage, and the conflict problem nobody draws: concurrent writes to two regions. The takeaway is grounded in latency math — what the speed of light does to synchronous replication and which designs cannot exist because of it.
Topics covered:
- Active-passive vs. active-active failure domains
- Cross-region replication paths for data stores
- Failover: DNS, routing, and read-only fallback
- Conflict handling and the latency floor of sync replication
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