SAA-C03 Design Resilient Architectures Practice Question
A financial services firm runs a latency-sensitive trading application on Amazon EC2 instances distributed across three Availability Zones behind a Network Load Balancer. The application must continue serving traffic with no manual intervention if an entire Availability Zone becomes impaired, and each instance must receive a fair share of connections. Which combination of features meets these requirements?
⚠ Common exam trap
The trap here is assuming that a Network Load Balancer distributes traffic evenly across zones by default; cross-zone load balancing must be enabled, and forgetting it can leave one zone carrying a disproportionate share.
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
✓
Enable cross-zone load balancing on the Network Load Balancer and register targets in all three Availability Zones
Cross-zone load balancing on a Network Load Balancer spreads incoming connections evenly across registered targets in all enabled Availability Zones, which is exactly what the fair-share requirement demands. Registering targets in three zones lets health checks detect an impaired zone and remove its targets so the remaining instances absorb traffic without operator action. The other options either bypass health checking, bind clients to single targets, or rely on slow DNS-based failover.
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 Network Load Balancer and register targets in all three Availability Zones
Why this is correct
Cross-zone load balancing on a Network Load Balancer distributes traffic evenly across registered targets in every enabled Availability Zone, so a single impaired zone does not concentrate load on the surviving instances. With targets registered in all three zones, the load balancer's health checks automatically remove unhealthy targets and continue routing to the rest. This delivers both even connection distribution and unattended zone-failure tolerance.
- ✗
Use an Application Load Balancer with sticky sessions enabled and register targets in all three Availability Zones
Why it's wrong here
Sticky sessions bind a client to one target, which undermines the fair-share distribution the scenario requires and can overload individual instances. An Application Load Balancer also operates at Layer 7, adding flexibility the trading workload does not need, and it does not provide the static, ultra-low-latency behavior expected from a Network Load Balancer. This choice does not satisfy the even-distribution requirement.
- ✗
Attach an Elastic IP address to each instance and have clients connect directly using a published list of addresses
Why it's wrong here
Direct client connections bypass the load balancer entirely, so there is no health checking, no automatic removal of an impaired Availability Zone, and no redistribution of connections. Clients would have to detect failure and choose another address themselves, which is manual intervention. This approach also distributes load based on client behavior rather than evenly across instances.
- ✗
Create a Network Load Balancer with one target group per Availability Zone and rely on DNS failover between the groups
Why it's wrong here
A Network Load Balancer routes to targets across its enabled zones automatically; separate target groups per zone with DNS failover introduce a manual, DNS-dependent mechanism that is not how the service is designed to operate. DNS caching also delays failover, so impaired-zone traffic could continue for the TTL duration. This adds complexity without meeting the fair-share or automatic-recovery requirements.
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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 Amazon Web Services exam blueprint
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