The answer is to place web and application tier instances in the same subnets across all three Availability Zones. This design is correct because it leverages the Application Load Balancer’s cross-zone load balancing (enabled by default) and the Network Load Balancer’s ability to route traffic to targets in the same AZ, ensuring that traffic between the ALB, NLB, and application instances stays within the same AZ whenever possible, directly reducing cross-AZ data transfer costs in a multi-tier web application. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this question tests your understanding of how AWS bills for inter-AZ traffic and the subtle difference between ALB and NLB routing behavior—a common trap is assuming you must place all tiers in a single AZ or use separate subnets, which would either sacrifice high availability or increase costs. A useful memory tip: “Same subnet, same AZ, same bill—keep traffic local to save your dollar.”
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is deploying a multi-tier web application on AWS. The application must be highly available across three Availability Zones. The web tier runs on EC2 instances behind an Application Load Balancer (ALB). The application tier runs on EC2 instances behind a Network Load Balancer (NLB). The database tier uses a Multi-AZ RDS instance. To reduce cross-AZ data transfer costs, which design should be implemented?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place web and application tier instances in the same subnets across all three AZs
Option D is correct because placing web and application tier EC2 instances in the same subnets across all three Availability Zones ensures that traffic between the ALB and NLB, as well as between the NLB and application instances, stays within the same AZ whenever possible. This design leverages the ALB's cross-zone load balancing behavior (enabled by default) and the NLB's ability to route traffic to targets in the same AZ, minimizing cross-AZ data transfer costs. AWS charges for data transfer between AZs, so keeping traffic within the same AZ reduces those costs while maintaining high availability across three AZs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use AWS Global Accelerator to reduce data transfer costs
Why it's wrong here
Global Accelerator improves performance but does not reduce internal cross-AZ costs.
✗
Place all web tier instances in one AZ and all application tier instances in another AZ
Why it's wrong here
This increases cross-AZ traffic and costs.
✗
Use a single AZ for all tiers to avoid cross-AZ traffic
Why it's wrong here
Single AZ reduces high availability.
✓
Place web and application tier instances in the same subnets across all three AZs
Why this is correct
ALB and NLB can route to targets in the same AZ, reducing cross-AZ traffic.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think placing all resources in a single AZ (Option C) is acceptable for cost savings, but the question explicitly requires high availability across three AZs, making that option invalid despite its cost advantage.
Detailed technical explanation
How to think about this question
Under the hood, an ALB with cross-zone load balancing enabled (default) distributes traffic evenly across all registered targets in all AZs, but the NLB by default does not enable cross-zone load balancing; when disabled, the NLB only routes traffic to targets in the same AZ as the client. By placing instances in the same subnets across AZs, the ALB can forward requests to application tier instances in the same AZ, and the NLB can then route to database tier instances in the same AZ, keeping traffic local. In a real-world scenario, if the web tier instances are in subnet A and application tier instances are in subnet B of the same AZ, traffic between them stays within the AZ, avoiding cross-AZ data transfer charges (currently $0.01/GB per direction).
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design for New Solutions — This question tests Design for New Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Place web and application tier instances in the same subnets across all three AZs — Option D is correct because placing web and application tier EC2 instances in the same subnets across all three Availability Zones ensures that traffic between the ALB and NLB, as well as between the NLB and application instances, stays within the same AZ whenever possible. This design leverages the ALB's cross-zone load balancing behavior (enabled by default) and the NLB's ability to route traffic to targets in the same AZ, minimizing cross-AZ data transfer costs. AWS charges for data transfer between AZs, so keeping traffic within the same AZ reduces those costs while maintaining high availability across three AZs.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is designing a multi-tier web application on AWS. The application requires high availability across multiple Availability Zones. Which AWS service should be used to distribute incoming traffic across multiple EC2 instances in different Availability Zones?
easy
A.AWS Global Accelerator
✓ B.Application Load Balancer
C.AWS Direct Connect
D.Amazon Route 53
Why B: An Application Load Balancer distributes incoming traffic across targets such as EC2 instances in multiple Availability Zones, providing high availability. Option A (AWS Global Accelerator) improves performance but is not the primary choice for multi-AZ distribution. Option C (Amazon Route 53) is a DNS service. Option D (AWS Direct Connect) is for dedicated network connections.
Variation 2. A company is designing a multi-tier web application on AWS. The application must be highly available and scale automatically based on traffic. The web tier runs on Amazon EC2 instances behind an Application Load Balancer. The application tier also uses EC2 instances. Which solution meets these requirements with the LEAST operational overhead?
medium
A.Use Amazon ECS with Fargate for both tiers, with an Application Load Balancer.
B.Use AWS Global Accelerator with a single Auto Scaling group for both tiers.
C.Use Network Load Balancer with Auto Scaling groups for both tiers.
✓ D.Use Auto Scaling groups for both web and application tiers, and route traffic through an Application Load Balancer.
Why D: Option A is correct because using Auto Scaling groups for both tiers and an ALB provides automatic scaling and high availability with minimal operational overhead. Option B is incorrect because AWS Global Accelerator does not provide automatic scaling of instances. Option C is incorrect because Amazon ECS adds container orchestration overhead. Option D is incorrect because a Network Load Balancer is not ideal for HTTP traffic and does not provide automatic scaling.
Last reviewed: Jun 24, 2026
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This SAP-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 SAP-C02 exam.
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