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CV0-004 Practice Question: A company uses a cloud load balancer to…
A company uses a cloud load balancer to distribute traffic to web servers. The load balancer health checks are failing for all instances. The instances are running and can be accessed directly via their private IPs from within the VPC. What is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates assume that because the instances are reachable via private IP from within the VPC, the load balancer should also be able to reach them, but they forget that the load balancer's health check traffic is subject to the instance's security group rules, which must explicitly permit the load balancer's source.
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 security group of the instances is not allowing traffic from the load balancer.
The most likely cause is that the security group attached to the web server instances does not include an inbound rule allowing traffic from the load balancer's source IP addresses or the load balancer's security group. Even though the instances are healthy and reachable via private IPs from within the VPC, the load balancer's health check probes (typically HTTP/HTTPS or TCP) are blocked by the instance-level firewall, causing all health checks to fail.
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 load balancer's cross-zone load balancing is disabled.
Why it's wrong here
Cross-zone load balancing affects traffic distribution, not health checks.
- ✗
The load balancer's listeners are configured on the wrong ports.
Why it's wrong here
Instances are accessible directly, so the port is likely correct.
- ✓
The security group of the instances is not allowing traffic from the load balancer.
Why this is correct
The load balancer sends health checks from a specific source; if the security group doesn't allow it, health checks fail.
- ✗
The instances are not registered with the target group.
Why it's wrong here
Health checks target registered instances; if they weren't registered, the load balancer would still fail but the error would indicate no targets.
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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.