DEA-C01 Data Store Management Practice Question
A company uses Amazon RDS for MySQL with Multi-AZ deployment. The primary instance fails, and automatic failover occurs. After failover, the application experiences higher latency. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume the DNS endpoint fails to update (Option C) or that the standby cannot handle writes (Option A), but AWS explicitly ensures both are handled correctly, and the real issue is the unavoidable cross-AZ network latency introduced by the new primary's location.
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 new primary instance is in a different Availability Zone, increasing network latency.
After a Multi-AZ failover in Amazon RDS for MySQL, the new primary instance is launched in a different Availability Zone (AZ) than the original primary. If the application's compute resources (e.g., EC2 instances) remain in the original AZ, cross-AZ network traffic incurs additional latency due to the physical distance and the need to traverse the AZ boundary, which typically adds 1–2 ms of round-trip time. This increased network latency directly impacts application performance, especially for latency-sensitive queries.
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 read replica is now the primary and cannot handle write traffic.
Why it's wrong here
Read replicas are not promoted during Multi-AZ failover.
- ✗
The failover process disabled automatic backups.
Why it's wrong here
Backups continue after failover.
- ✗
The DNS endpoint did not update to point to the new primary.
Why it's wrong here
DNS updates automatically during failover.
- ✓
The new primary instance is in a different Availability Zone, increasing network latency.
Why this is correct
Cross-AZ latency can be higher than same-AZ.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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