SOA-C02 Networking and Content Delivery Practice Question
A SysOps administrator has deployed an Application Load Balancer (ALB) that distributes traffic to a fleet of Amazon EC2 instances. The administrator notices that the ALB is sending all traffic to instances in a single Availability Zone (AZ), ignoring instances in other AZs. The ALB was created with default settings. Which action should the administrator take to ensure traffic is distributed evenly across all AZs?
⚠ Common exam trap
Candidates often believe cross-zone load balancing must be enabled on an Application Load Balancer. However, ALB cross-zone load balancing is always enabled by default (unlike Network Load Balancers, where it is disabled by default). When an ALB appears to ignore instances in other AZs, check target health checks and registration instead of cross-zone settings.
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
✓
Configure health checks on the target group to ensure unhealthy instances are not used.
By default, an Application Load Balancer has cross-zone load balancing always enabled, so traffic can be sent to healthy targets in any enabled Availability Zone. If traffic is not reaching instances in other AZs, the likely cause is that targets in those AZs are failing health checks or are not registered. Configuring accurate health checks on the target group will allow the ALB to mark those targets healthy and distribute traffic across all AZs. Connection draining and sticky sessions do not affect AZ-level distribution.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable cross-zone load balancing on the ALB.
Why it's wrong here
Cross-zone load balancing distributes incoming traffic across all instances in all AZs where the ALB is enabled. By default, it is enabled for Application Load Balancers, but if the administrator created the ALB with an older API or modified it, it may have been disabled. Enabling it will spread traffic evenly.
- ✗
Enable connection draining on the target group.
Why it's wrong here
Connection draining allows in-flight requests to complete when an instance is deregistered or unhealthy. It does not affect how traffic is distributed across AZs.
- ✗
Enable sticky sessions (session stickiness) on the target group.
Why it's wrong here
Sticky sessions make the load balancer send requests from a particular client to the same instance. It can cause uneven distribution if not carefully balanced, and it does not solve the problem of traffic only going to one AZ.
- ✓
Configure health checks on the target group to ensure unhealthy instances are not used.
Why this is correct
Health checks ensure traffic is only sent to healthy instances, but they do not control the AZ-level distribution. If all instances are healthy, the ALB will still only send traffic to instances in the same AZ as the node that received the request if cross-zone is disabled.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services 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 SOA-C02 exam.