CV0-004 Troubleshooting Practice Question
A company runs a critical e-commerce application on a cloud platform. The architecture includes a load balancer in front of an auto scaling group of compute instances across two availability zones. The instances are in a private subnet and use a NAT gateway for outbound internet access. The application stores session data in a managed Redis cache cluster. During a flash sale, users report that the site is extremely slow and some requests time out. Monitoring shows the load balancer's latency metric is high, and the number of healthy hosts fluctuates. The CPU utilization on the compute instances averages 60% and memory averages 70%. The Redis cluster's CPU utilization is 90%, and its memory usage is 95%. The NAT gateway's metrics show high BytesOutToSource but no errors. Which of the following is the most likely cause of the performance issue?
⚠ Common exam trap
The trap here is that candidates may focus on the NAT gateway or auto scaling group because they are common bottlenecks, but the key clue is the Redis cluster's high CPU and memory metrics, which directly correlate with session store performance issues in a stateful application.
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 managed Redis cache cluster is overloaded and becoming a bottleneck for session lookups
The managed Redis cache cluster is the most likely bottleneck because its CPU utilization is at 90% and memory usage at 95%, indicating it is near capacity. Since the application stores session data in Redis, high latency and timeouts during a flash sale are consistent with an overloaded session store that cannot keep up with request volume, causing the load balancer to experience increased latency and healthy host fluctuations as sessions fail to be retrieved or written.
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 NAT gateway is throttling traffic due to bandwidth limits
Why it's wrong here
NAT gateway bandwidth throttling would surface as connection errors or dropped packets, yet the metrics show no errors and the Redis cluster sits at 90% CPU and 95% memory — the actual bottleneck. NAT gateways are sized for outbound throughput, so this option would fit a scenario where private-subnet egress saturated while backend caches stayed healthy.
- ✓
The managed Redis cache cluster is overloaded and becoming a bottleneck for session lookups
Why this is correct
Redis CPU at 90% and memory at 95% indicate the cache cluster is saturated, so session lookups slow or fail, cascading into high load balancer latency and fluctuating healthy hosts. This satisfies the observed bottleneck, since compute CPU and memory remain moderate.
- ✗
The auto scaling group is not scaling quickly enough due to cooldown periods
Why it's wrong here
Cooldown periods delay additional scaling actions, but the compute instances average only 60% CPU, so they are not saturated; the Redis cluster at 90% CPU and 95% memory is the bottleneck. It is tempting because fluctuating healthy hosts suggest scaling churn, yet the cache saturation explains the latency.
- ✗
The load balancer's idle timeout setting is too low, causing premature connection drops
Why it's wrong here
An idle timeout closes connections that stay inactive too long, but it would not raise Redis CPU to 90% or memory to 95%, nor make healthy host counts fluctuate. It is tempting because timeouts match the reported symptoms, yet the cache cluster's saturation is the actual constraint.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.