DVA-C02 Development with AWS Services Practice Question
This DVA-C02 practice question tests your understanding of development with aws services. 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 runs a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application stores user session data in an Amazon ElastiCache for Redis cluster. Recently, users have been experiencing intermittent session timeouts and data loss. The developer examines the application logs and finds errors indicating that the Redis cluster is returning 'READONLY You can't write against a read-only replica.' The ElastiCache cluster is configured as a Redis replication group with one primary and two replicas. The application's connection code uses the primary endpoint. What is the most likely cause of this issue?
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
✓
A failover event occurred, and the application is still trying to write to the old primary node, which is now a replica.
Option A is correct because a failover event may have promoted one of the replicas to become the new primary. The application might have cached the old primary endpoint IP, or the DNS TTL could cause the application to still connect to the old primary (now a replica). Writing to a replica results in the READONLY error. Option B is incorrect because ElastiCache does not automatically scale down. Option C is incorrect because ElastiCache cluster mode is for sharding, not primary-replica. Option D is incorrect because security groups block connections entirely, not cause intermittent writes.
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 ElastiCache cluster has been scaled down to a single node, causing the primary to become unavailable.
Why it's wrong here
Incorrect: Scaling down would change the cluster, but not cause READONLY errors.
✓
A failover event occurred, and the application is still trying to write to the old primary node, which is now a replica.
Why this is correct
Correct: After failover, the old primary becomes a replica and rejects writes.
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.
✗
The ElastiCache security group is blocking write traffic to the primary endpoint.
Why it's wrong here
Incorrect: Security groups block all traffic, not just writes.
✗
The Redis cluster mode is enabled, and the application is not using the correct cluster endpoint.
Why it's wrong here
Incorrect: Cluster mode is for sharding; the issue is with primary-replica.
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
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 DVA-C02 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.
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A failover event occurred, and the application is still trying to write to the old primary node, which is now a replica. — Option A is correct because a failover event may have promoted one of the replicas to become the new primary. The application might have cached the old primary endpoint IP, or the DNS TTL could cause the application to still connect to the old primary (now a replica). Writing to a replica results in the READONLY error. Option B is incorrect because ElastiCache does not automatically scale down. Option C is incorrect because ElastiCache cluster mode is for sharding, not primary-replica. Option D is incorrect because security groups block connections entirely, not cause intermittent writes.
What should I do if I get this DVA-C02 question wrong?
Identify which DVA-C02 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", "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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