DBS-C01 Management and Operations Practice Question
An e-commerce company runs a multi-AZ deployment of Amazon RDS for MySQL. During a recent failover test, the application experienced a 30-second write outage. The application uses a connection pooling library. The DB instance has a 60-second TTL for DNS records. What is the MOST likely cause of the outage?
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 connection pool had open connections to the old primary, and DNS TTL caused a delay in reconnecting to the new primary.
During a Multi-AZ failover, the RDS DNS record is automatically updated to point to the new primary. However, the application's connection pool may still have open connections to the old primary IP. Because the DNS TTL is 60 seconds, the client may continue to resolve to the old (cached) IP for up to 60 seconds, causing a write outage until connections are re-established to the new primary. Option B is incorrect because a cold start typically refers to an application starting from scratch, which is not the case here. Option C is incorrect because the DNS record is indeed updated after failover; the issue is client-side caching. Option D is incorrect because Multi-AZ failover usually completes within 1-2 minutes, but the outage duration is determined by DNS TTL and connection pooling behavior, not the failover time itself.
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 connection pool had open connections to the old primary, and DNS TTL caused a delay in reconnecting to the new primary.
Why this is correct
Stale connections and DNS caching can cause a brief outage until connections are refreshed.
- ✗
The application experienced a cold start after the failover.
Why it's wrong here
Cold start is not related to database failover.
- ✗
The DNS record for the RDS endpoint was not updated after the failover.
Why it's wrong here
RDS automatically updates the DNS CNAME to point to the new primary.
- ✗
The Multi-AZ failover took longer than 30 seconds to complete.
Why it's wrong here
Multi-AZ failover usually completes within 1-2 minutes, but the outage was only 30 seconds.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.