Question 62 of 977
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?
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.
When the load balancer is configured to distribute traffic across all zones, it should balance traffic across all availability zones. However, if instances in other zones fail health checks, they are marked as unhealthy and removed from the rotation, causing all traffic to go to healthy instances in only one zone. Option A is incorrect because firewall rules are not zone-specific; they apply to resources regardless of zone. Option C is incorrect because route tables affect outbound traffic from instances, not load balancer traffic distribution. Option D is incorrect because a single backend pool can contain instances from multiple zones; this does not limit traffic to one zone.
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 are not zone-specific; they apply to resources regardless of zone.
- ✓
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
Route tables affect outbound traffic from instances, not load balancer traffic distribution.
- ✗
The listener rules are configured to forward traffic to a single backend pool.
Why it's wrong here
A single target group can contain instances from multiple zones; this does not limit traffic to one zone.
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Last reviewed: Jun 24, 2026
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