DEA-C01 Data Store Management Practice Question
A company is using Amazon RDS for MySQL with Multi-AZ deployment. They notice that during a recent failover test, the application experienced a brief write outage. The application uses a connection string that points to the RDS instance endpoint. What is the MOST likely cause of the write outage?
⚠ Common exam trap
Candidates often confuse the RDS instance endpoint with the cluster endpoint used in Amazon Aurora, assuming that Multi-AZ automatically provides a seamless, zero-downtime failover for writes, when in fact the instance endpoint requires DNS propagation and connection re-establishment.
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 is using the RDS instance endpoint instead of the cluster endpoint, so it does not automatically route to the standby after failover.
In a Multi-AZ RDS deployment, the instance endpoint always points to the current primary instance. During a failover, the DNS record for the instance endpoint is updated to point to the new primary, but existing connections to the old primary are dropped, and the DNS change can take time to propagate. The application's connection string using the instance endpoint means it does not automatically route to the standby during the failover transition, causing a brief write outage until the DNS update completes and the application reconnects. In contrast, using a cluster endpoint (available for Aurora, not standard RDS) or implementing retry logic in the application would mitigate this.
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 is using a read replica endpoint, which does not support write operations.
Why it's wrong here
Read replicas are for read traffic only and are not used for failover.
- ✓
The application is using the RDS instance endpoint instead of the cluster endpoint, so it does not automatically route to the standby after failover.
Why this is correct
The instance endpoint is static and remains pointed to the original primary; after failover, the application must reconnect to the new primary using the CNAME which takes time to update.
- ✗
The application is connecting through a Network Load Balancer, which is not configured for cross-zone failover.
Why it's wrong here
Multi-AZ RDS does not use a load balancer; the failover is handled by DNS CNAME update.
- ✗
The application connection pool is exhausted because the failover caused all existing connections to drop simultaneously.
Why it's wrong here
While connections drop, the outage is due to the endpoint not redirecting writes, not connection pool exhaustion.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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