Interview › Databases & Caching
Can a read replica be in a different region, and why would you do that?
Databases & Caching · Basic level
Answer
Multi-AZ protects the writer for HA and failover; read replicas are readable copies used for read scaling, reporting, migration, and DR. Read replicas are generally asynchronous, can lag, can often be cross-Region, and can be promoted to standalone databases when needed.
Technical explanation
Use Multi-AZ for availability and read replicas for read workload isolation or migration targets.
Replica lag means read-your-writes is not guaranteed from replicas.
Cross-Region replicas are useful for DR and locality, but require RPO/RTO, secrets, DNS, KMS, and failover runbooks.
Hands-on example
Read/write routing example:
POST /orders -> primary endpoint
GET /orders/{id} immediately after create -> primary endpoint
GET /orders/report -> read replica endpoint
Promotion command for migration or DR:
$ aws rds promote-read-replica --db-instance-identifier orders-replica-dr
Before promotion, check replica lag and stop writes if a clean cutover is required.
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More Databases & Caching interview questions
- What is Amazon RDS, and what does it manage for you versus self-managed databases?
- What database engines does RDS support?
- What is the difference between RDS and Aurora?
- What is Multi-AZ in RDS, and how does automatic failover work?
- How long does an RDS Multi-AZ failover typically take, and what triggers it?
- What is the difference between Multi-AZ and a read replica?
- When would you use a read replica, and can it become a standalone database?
- What is the difference between automated backups and manual snapshots in RDS?