- A
The connection pool had open connections to the old primary, and DNS TTL caused a delay in reconnecting to the new primary.
Stale connections and DNS caching can cause a brief outage until connections are refreshed.
- B
The application experienced a cold start after the failover.
Why wrong: Cold start is not related to database failover.
- C
The DNS record for the RDS endpoint was not updated after the failover.
Why wrong: RDS automatically updates the DNS CNAME to point to the new primary.
- D
The Multi-AZ failover took longer than 30 seconds to complete.
Why wrong: Multi-AZ failover usually completes within 1-2 minutes, but the outage was only 30 seconds.
Question 1,498 of 1,730
Understanding Write Outages During RDS Multi-AZ Failover
This DBS-C01 practice question tests your understanding of management and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.
The correct answer is A. 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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
Visual reference
Quick reference
Common DNS Record Types
| Record | Purpose | Example |
|---|---|---|
| A | IPv4 address mapping | example.com → 93.184.216.34 |
| AAAA | IPv6 address mapping | example.com → 2606:2800::1 |
| CNAME | Alias to another hostname | www → example.com |
| MX | Mail server for domain | example.com → mail.example.com (priority 10) |
| TXT | Text data (SPF, DKIM, verification) | v=spf1 include:_spf.example.com ~all |
| NS | Authoritative name servers | example.com NS ns1.example.com |
| PTR | Reverse DNS (IP → hostname) | 34.216.184.93.in-addr.arpa → example.com |
| SOA | Zone authority record | Primary NS, admin email, serial, TTL defaults |
What to study next
Got this wrong? Here's your next step.
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this DBS-C01 question test?
Management and Operations — This question tests Management and Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The connection pool had open connections to the old primary, and DNS TTL caused a delay in reconnecting to the new primary. — The correct answer is A. 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.
What should I do if I get this DBS-C01 question wrong?
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 20, 2026
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