Interview › Databases & Caching
What is Multi-AZ in RDS, and how does automatic failover work?
Databases & Caching · Basic level
Answer
RDS Multi-AZ is a high-availability deployment where RDS maintains a standby or alternate writer in another Availability Zone and automatically fails over when the primary cannot serve safely. Traditional Multi-AZ DB instance failover is commonly around 60 to 120 seconds, but application recovery can be longer.
Technical explanation
Multi-AZ is for availability, not read scaling in the traditional DB instance model.
Failover can be triggered by infrastructure failure, AZ disruption, maintenance, storage/network issues, or manual reboot with failover.
Applications must reconnect, retry idempotently, respect DNS, and handle in-flight transaction failure.
Hands-on example
Staging failover test:
$ while true; do date; psql "$DB_URL" -c "select now();" && echo ok || echo failed; sleep 1; done
$ aws rds reboot-db-instance --db-instance-identifier orders-stage --force-failover
Measure first failure, first success after recovery, API 5xx, p95 latency, and whether any pod restart was 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?
- 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?
- Can a read replica be in a different region, and why would you do that?
- What is the difference between automated backups and manual snapshots in RDS?