SAA-C03 Design Cost-Optimized Architectures Practice Question
A team runs an Amazon NLB in a VPC with targets registered in multiple Availability Zones (AZs). Their bill shows high inter-AZ data transfer charges. They want to reduce unnecessary cross-AZ traffic costs while still maintaining healthy targets per AZ. What change is most likely to reduce inter-AZ charges?
⚠ Common exam trap
A common mix-up: candidates assume enabling cross-zone load balancing always reduces costs or improves performance, but for NLB it actually increases inter-AZ data transfer charges, and the question specifically asks for cost reduction, not high availability.
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
✓
Disable cross-zone load balancing on the NLB so each client is routed to targets in the same AZ when possible.
Disabling cross-zone load balancing on an NLB ensures that each client is routed only to targets within the same Availability Zone as the NLB node that receives the traffic. This eliminates inter-AZ data transfer charges because traffic never leaves the AZ boundary. The NLB still maintains healthy targets per AZ by distributing traffic only among healthy targets within that AZ.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Disable cross-zone load balancing on the NLB so each client is routed to targets in the same AZ when possible.
Why this is correct
Disabling cross-zone load balancing helps keep traffic within the same AZ, reducing inter-AZ data transfer charges.
- ✗
Enable cross-zone load balancing so all targets receive traffic from every AZ.
Why it's wrong here
Enabling cross-zone generally increases cross-AZ traffic and can raise inter-AZ transfer costs.
When this WOULD be correct
In a scenario where you need to ensure even traffic distribution across all targets regardless of AZ, and cost is not a primary concern, enabling cross-zone load balancing would be correct. For example, if you have uneven target capacity across AZs and need to prevent overloading a single AZ.
- ✗
Move the NLB to a different Region so traffic is always kept local.
Why it's wrong here
Changing Region does not eliminate inter-AZ traffic within the new Region and can add Region transfer costs.
When this WOULD be correct
In a scenario where the question asks how to reduce data transfer costs between two different AWS Regions, and the application can tolerate higher latency, moving the NLB to the same Region as the clients would eliminate cross-Region data transfer charges.
- ✗
Replace the NLB with a NAT gateway to reduce data charges between AZs.
Why it's wrong here
NAT gateways affect egress to the internet; they do not control inter-AZ routing for load balancer traffic.
When this WOULD be correct
In a scenario where a team needs to provide outbound internet access to instances in private subnets and wants to reduce data transfer costs by ensuring traffic stays within a single AZ (e.g., by deploying a NAT Gateway per AZ), this option would be correct.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Disable cross-zone load balancing on the NLB so each client is routed to targets in the same AZ when possible.Correct answer▾
Why this is correct
Disabling cross-zone load balancing helps keep traffic within the same AZ, reducing inter-AZ data transfer charges.
✗Enable cross-zone load balancing so all targets receive traffic from every AZ.Wrong answer — click to see why▾
Why this is wrong here
Enabling cross-zone load balancing would increase inter-AZ traffic because the NLB would distribute requests across all AZs, incurring higher data transfer charges, which is the opposite of the goal to reduce costs.
★ When this WOULD be the correct answer
In a scenario where you need to ensure even traffic distribution across all targets regardless of AZ, and cost is not a primary concern, enabling cross-zone load balancing would be correct. For example, if you have uneven target capacity across AZs and need to prevent overloading a single AZ.
Why candidates choose this
Candidates may confuse cross-zone load balancing with a feature that reduces costs, or they might think that distributing traffic more evenly always optimizes performance, overlooking the inter-AZ data transfer charges.
✗Move the NLB to a different Region so traffic is always kept local.Wrong answer — click to see why▾
Why this is wrong here
Moving the NLB to a different Region does not reduce inter-AZ data transfer charges; it would increase costs due to cross-Region traffic and latency, and does not address the issue of cross-AZ traffic within the original VPC.
★ When this WOULD be the correct answer
In a scenario where the question asks how to reduce data transfer costs between two different AWS Regions, and the application can tolerate higher latency, moving the NLB to the same Region as the clients would eliminate cross-Region data transfer charges.
Why candidates choose this
Candidates may think that moving to a different Region could localize traffic and reduce costs, misunderstanding that inter-AZ charges are within a Region, not between Regions.
✗Replace the NLB with a NAT gateway to reduce data charges between AZs.Wrong answer — click to see why▾
Why this is wrong here
A NAT Gateway is used for outbound internet traffic from private subnets, not for load balancing traffic between AZs. Replacing an NLB with a NAT Gateway would not reduce inter-AZ data charges and would break the load balancing functionality.
★ When this WOULD be the correct answer
In a scenario where a team needs to provide outbound internet access to instances in private subnets and wants to reduce data transfer costs by ensuring traffic stays within a single AZ (e.g., by deploying a NAT Gateway per AZ), this option would be correct.
Why candidates choose this
Candidates may mistakenly think that a NAT Gateway can replace an NLB for internal traffic or that it inherently reduces cross-AZ costs, confusing its purpose of providing internet access with load balancing.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 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 SAA-C03 exam.