SAA-C03 Design Resilient Architectures Practice Question
An internal service is hosted behind an Application Load Balancer (ALB) with targets spread across two Availability Zones. If the targets in one Availability Zone become unhealthy, the service must continue serving traffic from the healthy AZ. What change most directly improves resilience at the load-balancing layer?
⚠ Common exam trap
It's easy for candidates to think SQS decoupling (Option D) improves resilience at the load-balancing layer, but SQS operates at the application layer and does not affect how the ALB routes traffic to unhealthy targets.
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 target group health checks so the ALB stops sending traffic to unhealthy targets and continues routing to healthy targets in the other Availability Zone.
Configuring target group health checks allows the ALB to automatically detect unhealthy targets and stop sending traffic to them, while continuing to route requests to healthy targets in the other Availability Zone. This directly improves resilience at the load-balancing layer by ensuring traffic is only forwarded to healthy instances, maintaining service availability even when an entire AZ fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Turn off health checks and rely only on instance CPU utilization to route traffic.
Why it's wrong here
ALB routing depends on target health as determined by health checks. Turning health checks off prevents the ALB from detecting and removing unhealthy targets from service, so traffic can still be routed to failing targets.
- ✗
Configure ALB listener rules to route all traffic to a single target group in one Availability Zone.
Why it's wrong here
Restricting the ALB listener to route all traffic to a single target group in one Availability Zone eliminates the multi-AZ redundancy that the load balancer is designed to provide. If that Availability Zone experiences an outage or the targets within it become unhealthy, the ALB has no healthy targets in another zone to fail over to, leaving the internal service unreachable. Even if health checks are functioning normally, this configuration makes the application's availability dependent entirely on one zone, contrary to the requirement to keep serving traffic from healthy targets in the other AZ.
- ✓
Configure target group health checks so the ALB stops sending traffic to unhealthy targets and continues routing to healthy targets in the other Availability Zone.
Why this is correct
With target group health checks enabled and configured correctly, the ALB evaluates each target's health and stops routing requests to targets marked unhealthy. As long as healthy targets exist in the other AZ, the ALB preserves reachability.
- ✗
Store requests in an SQS queue before routing them to the ALB.
Why it's wrong here
SQS can decouple producers and consumers and provide buffering, but it does not change how the ALB determines target health or decides which targets receive traffic. The stated requirement focuses on load-balancing behavior when targets become unhealthy.
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