Multi-Region Active-Active Readiness Checklist

Most multi-region setups are active-passive in disguise. The 10 capabilities required for true active-active.

Data layer

Multi-region active-active is one of the most complex architectural patterns to operate. Many teams claim active-active and have not actually verified the claim under failure conditions. The readiness check is the structured assessment of whether the architecture would actually behave correctly when one region fails.

What the data layer requires:

• Multi-region writeable database.: The database must accept writes in every region. CockroachDB, Spanner, DynamoDB Global Tables, Cassandra with multi-region replication. The database is the foundation; without multi-region writes, the rest of the architecture cannot be active-active.
• Conflict resolution strategy.: When concurrent writes target the same data, conflict resolution determines the outcome. Last-write-wins is simplest; CRDTs are mathematically clean; application-level merge logic is most flexible. The choice matches the data class.
• Replication topology documented.: Each region's role and replication relationships are documented. The team understands the data flow; failure of any region's replication path is a known scenario with a known remediation.
• Schema changes coordinated.: Multi-region active-active makes schema changes harder. Migrations must apply consistently across regions; partial application produces conflicts. The team has a documented schema change process that respects the topology.
• Replica lag monitored.: The lag between regions is the canary for replication health. Lag spikes indicate problems; sustained lag indicates capacity or network issues. The monitoring is per-region-pair; the team sees which links are healthy.

The data layer is the foundation of active-active readiness. Without it, the rest of the architecture is theater.

Traffic layer

The traffic layer determines how user requests reach the right region. In active-active, this layer must support graceful degradation when a region fails: traffic must redistribute to healthy regions without manual intervention.

• Geo-aware DNS routing.: Route 53, Cloud DNS, or similar provides geo-aware routing. Users are routed to the nearest healthy region by default; the routing adapts based on health checks and routing policies.
• Health checks per region.: Each region has health checks that determine whether it is eligible to receive traffic. The health checks cover the application stack end-to-end; not just network reachability but actual service health.
• Failover criteria documented.: The team documents what triggers a traffic shift. Network failure, application errors above a threshold, manual operator intervention. The criteria are explicit; ambiguity in failover decisions leads to slow or wrong responses during incidents.
• What triggers traffic shift.: Each trigger is operationally tested. The team verifies that the documented trigger actually causes the documented response. Triggers that work on paper but fail under real conditions are caught before they matter.
• Drain procedures.: Active region drain (planned removal from the rotation) is a documented procedure. The drain produces orderly traffic redistribution; the readiness check verifies the procedure works.

The traffic layer is the visible part of active-active. Users see traffic moving between regions; the engineering team sees the routing changes.

Test it

The readiness check is not complete without periodic testing. Architecture that has never been tested under failure is unproven; the assumption that it works does not survive contact with a real incident.

• Quarterly: drain one region.: Once per quarter, drain a region from the active rotation. Traffic should redistribute to remaining regions; the system should continue operating; alerts should be controlled and informative.
• Traffic should redistribute without alarm.: The drain should be a non-event. The system handles it; the team observes; no customer-visible degradation occurs. If the drain produces alarms or degradation, the architecture has gaps that need closing.
• Without testing, multi-region is theater.: Architectures that are claimed but never tested fail in their first real test. The cost of finding the gaps under controlled conditions is far lower than finding them during an actual outage.
• Test scenarios beyond region failure.: Region failure is the headline case; the readiness check tests other scenarios too. Network partition between regions; database replication failure; partial degradation of one region. Each is a different failure mode with a different expected response.
• Document and fix gaps.: Each test produces a report. Gaps are tracked through to closure. The next test verifies the closure. The discipline produces continuous improvement; the architecture gets stronger over time.

Multi-region active-active readiness is the discipline that distinguishes claimed multi-region from actual multi-region. Nova AI Ops integrates with multi-region health data, runs quarterly drain checks, and produces the readiness report that the team and leadership both need to trust the architecture.