SOA-C02 Reliability and Business Continuity Practice Question
A company has an RDS PostgreSQL database with a Multi-AZ deployment. The primary instance fails. What happens to the application connections?
⚠ Common exam trap
Candidates often confuse Multi-AZ failover with read replicas, assuming the application is automatically redirected to a read replica for writes, but read replicas are asynchronous and cannot accept write traffic.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application must reconnect to the same endpoint; it will be redirected to the standby instance.
When the primary RDS PostgreSQL instance fails in a Multi-AZ deployment, AWS automatically fails over to the standby instance in a different Availability Zone. The DNS endpoint (CNAME) remains the same, but its resolution is updated to point to the standby instance's IP address. The application must reconnect to the same endpoint, as existing connections to the failed primary are dropped; after reconnection, traffic is seamlessly routed to the new primary.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The application must reconnect to the same endpoint; it will be redirected to the standby instance.
Why this is correct
In a Multi-AZ RDS deployment, a standby DB instance is provisioned in a different Availability Zone and is kept in sync with the primary via synchronous replication. When a failure occurs, Amazon RDS automatically promotes the standby and updates the DNS record for the same endpoint to point to the new primary. Existing application connections are dropped, so the application must reconnect, but it must reconnect to the same endpoint; the DNS update happens automatically and transparently to the client.
- ✗
The application will be automatically redirected to a read replica.
Why it's wrong here
A read replica is a separate DB instance with its own endpoint and serves only read traffic; it does not participate in Multi-AZ failover as a standby. During Multi-AZ failover, RDS promotes the synchronized standby in another Availability Zone, not any read replica. Read replicas are used for offloading read queries or for manual promotion in disaster recovery scenarios, but the application will never be automatically redirected to a read replica for a Multi-AZ failover event.
- ✗
The administrator must manually change the CNAME to point to the standby.
Why it's wrong here
Amazon RDS automatically manages the DNS/CNAME record for a Multi-AZ instance. When a failover occurs, RDS changes the CNAME to resolve to the standby instance's private IP address without requiring any administrator intervention. Manually changing the CNAME would be both unnecessary and contrary to RDS's managed service model, and doing so could break connectivity or cause certificate/DNS validation issues because RDS already handles this update as part of the failover process.
- ✗
The application must use a new endpoint in a different AWS Region.
Why it's wrong here
Multi-AZ deployments are designed to provide high availability within a single AWS Region by deploying a standby in a different Availability Zone (AZ) of that same Region. The database endpoint remains the same across failover within the Region; it does not change to a new Regional endpoint. Moving to a different AWS Region would require cross-Region capabilities such as a global database or manual replica promotion, which are not part of the Multi-AZ failover behavior described in this scenario.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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