CV0-004 Troubleshooting Practice Question
A web application is deployed across multiple availability zones behind a load balancer. The administrator notices that all traffic is being routed to instances in only one availability zone, causing performance issues. The load balancer is configured to distribute traffic across all zones evenly. What is the most likely cause?
⚠ Common exam trap
CV0-004 often tests the assumption that even load balancer configuration guarantees even traffic distribution — candidates overlook that health check status dynamically removes backends, so runtime health, not configuration, explains uneven routing.
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 instances in the other zones are marked as unhealthy due to failing health checks.
If the load balancer is configured to distribute traffic evenly across all availability zones but traffic only reaches one zone, the most likely cause is that instances in the other zones are failing health checks and are marked unhealthy. Load balancers only route to healthy backends, so unhealthy instances in other zones are excluded, concentrating traffic in the one healthy zone. This matches the symptom of uneven distribution despite even configuration.
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 firewall rules for the load balancer only allow traffic from one zone.
Why it's wrong here
Security groups and firewall rules filter by port, protocol and source CIDR, not by availability zone, so a rule cannot target one zone alone. Firewall configuration is the right area to examine when specific source addresses or ports are blocked, not when zone distribution is skewed.
- ✓
The instances in the other zones are marked as unhealthy due to failing health checks.
Why this is correct
When cross-zone load balancing is enabled, the load balancer should distribute traffic across all availability zones. However, if instances in other zones fail health checks, they are marked as unhealthy and removed from the target group's rotation, causing all traffic to go to healthy instances in only one zone.
- ✗
The route table for the subnets in the other zones is missing a default route.
Why it's wrong here
A missing default route in the other subnets would break outbound internet access, not inbound load balancer distribution; the load balancer still routes to healthy registered targets. Route tables matter when instances must reach external endpoints, such as patching or calling APIs, not for spreading incoming traffic across zones.
- ✗
The listener rules are configured to forward traffic to a single backend pool.
Why it's wrong here
Listener rules matching a single target group would send all traffic to one backend pool, but the stem states the load balancer is configured to distribute evenly across zones, so this contradicts the given configuration. Listener rules are the correct focus when path- or host-based routing to distinct target groups is required.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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.