DEA-C01 Multi-AZ deployment Practice Question
A company is using Amazon RDS for PostgreSQL with Multi-AZ deployment. The primary instance fails and a failover occurs. After the failover, the application cannot connect to the database. What is the MOST likely cause?
⚠ Common exam trap
Many candidates assume security groups or instance state are the issue, but AWS explicitly tests the concept that the RDS CNAME is the correct connection target and that hardcoding endpoints leads to failover failures.
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 old primary instance endpoint instead of the RDS CNAME.
After a Multi-AZ failover in Amazon RDS for PostgreSQL, the DNS CNAME record automatically updates to point to the new primary instance in the standby Availability Zone. If the application hardcodes the old primary instance's endpoint (specific IP or DNS name) instead of using the RDS CNAME (which remains constant), it will attempt to connect to the failed instance, causing connectivity loss. The CNAME is the stable connection point that always resolves to the current primary instance.
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 database instance is in a 'stopped' state after failover.
Why it's wrong here
After failover, the new primary becomes available.
- ✗
The Multi-AZ failover requires manual intervention to complete.
Why it's wrong here
Multi-AZ failover is automatic.
- ✗
The security group for the RDS instance was not updated during failover.
Why it's wrong here
Security groups are attached to the instance, which remains the same.
- ✓
The application is using the old primary instance endpoint instead of the RDS CNAME.
Why this is correct
The application should use the CNAME, which updates automatically after failover.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.