DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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.
A company is using Amazon RDS for MySQL with Multi-AZ deployment. The database experiences a failover due to an availability zone outage. After the failover, the application team reports that the database endpoint is not resolving to the new primary. What is the most likely reason?
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.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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 a cached DNS resolution that points to the old primary.
Option D is correct because after an RDS Multi-AZ failover, the DNS CNAME record for the DB instance is updated to point to the new primary in the standby AZ. However, if the application or its DNS resolver has cached the previous DNS resolution, it will continue to use the old IP address, which is no longer reachable. This is a common issue that can be resolved by reducing the TTL on the DNS record or implementing retry logic with DNS re-resolution in the application.
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 RDS CNAME record was not updated by AWS after the failover.
Why it's wrong here
AWS automatically updates the CNAME to point to the new primary.
✗
The application is using the read replica endpoint instead of the primary endpoint.
Why it's wrong here
Read replica endpoints are separate and not affected by failover.
✗
The application is using a Route 53 health check that failed and redirected traffic away from the endpoint.
Why it's wrong here
Route 53 health checks are not automatically configured for RDS endpoints.
✓
The application is using a cached DNS resolution that points to the old primary.
Why this is correct
DNS caching can cause the old IP to be used until the TTL expires.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume AWS automatically handles DNS propagation instantly or that the CNAME record is not updated, but the real issue is client-side DNS caching, which is a common operational oversight in failover scenarios.
Detailed technical explanation
How to think about this question
RDS Multi-AZ failover works by promoting the standby instance in a different AZ to primary and updating the DNS CNAME record for the DB instance endpoint. The DNS TTL for RDS endpoints is typically set to 30 seconds, but client-side DNS caching (e.g., in the OS resolver, Java DNS cache, or application-level cache) can ignore this TTL and retain the old IP for longer. For example, the Java Virtual Machine (JVM) caches DNS lookups indefinitely by default unless the networkaddress.cache.ttl property is set, which can cause prolonged outages after a failover.
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.
TExam Day Tips
→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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The application is using a cached DNS resolution that points to the old primary. — Option D is correct because after an RDS Multi-AZ failover, the DNS CNAME record for the DB instance is updated to point to the new primary in the standby AZ. However, if the application or its DNS resolver has cached the previous DNS resolution, it will continue to use the old IP address, which is no longer reachable. This is a common issue that can be resolved by reducing the TTL on the DNS record or implementing retry logic with DNS re-resolution in the application.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "primary". 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.
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Question Discussion
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