Geo-replication & Multi-region
As systems scale globally, users expect low latency and high availability regardless of location.
Geo-replication and multi-region deployments are key strategies to meet these goals.
1. What is Geo-replication?
- Replicating data across multiple geographic regions.
- Ensures users get data from the nearest location.
- Provides redundancy in case of regional outages.
2. Benefits of Multi-region Systems
Low Latency
- Users served from nearest data center.
- Example: AWS, GCP, Azure have regional deployments.
Fault Tolerance
- Survive region-wide outages (disasters, power loss, etc.).
- Example: Active-active across US-East & US-West.
Regulatory Compliance
- Data residency laws (GDPR, HIPAA).
- Keep data within country/region.
Scalability
- Distribute workload across multiple regions.
3. Deployment Models
3.1 Active-Passive (DR Setup)
- One primary region handles all traffic.
- Secondary region is standby (disaster recovery).
- Simple, cheaper, but slower failover.
3.2 Active-Active (Global)
- Multiple regions serve traffic simultaneously.
- Users automatically routed to nearest region.
- Requires conflict resolution & consensus.
- More complex, but better performance & availability.
4. Challenges
- Consistency: keeping replicas in sync across regions.
- Latency: synchronous replication across continents is slow.
- Conflict resolution: when writes happen in different regions.
- Cost: cross-region replication and infra costs.
5. Real-World Examples
- Google Spanner → global DB with synchronous replication, strong consistency.
- AWS DynamoDB Global Tables → async replication, eventual consistency.
- Azure Cosmos DB → tunable consistency (5 levels).
6. Interview Tips
- Mention geo-replication for global user bases.
- Say: “I’d use multi-region active-active for global apps, but active-passive for simpler DR setups.”
- Tie it to CAP/PACELC: global systems often trade latency for consistency.
- Bring up compliance (GDPR) if relevant.
7. Diagram
[ User in Europe ] --> EU Data Center
[ User in US ] ----> US Data Center
Data synced between regions (sync/async).8. Next Steps
- Learn about Graceful Degradation.
- Explore Circuit Breakers, Retries, Timeouts.