How to Reduce Cross-AZ Data Transfer Costs in a Multi-Tier Web Application
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?
⚠ Common exam trap
Many exam-takers confuse DNS-based routing (Route 53) with actual load balancing, but Route 53 only provides DNS resolution and does not actively distribute traffic across instances or perform health checks at the application layer.
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
✓
Application Load Balancer
The Application Load Balancer (ALB) operates at Layer 7 of the OSI model and is designed to distribute incoming HTTP/HTTPS traffic across multiple targets, such as EC2 instances, in different Availability Zones. By registering instances in multiple AZs and enabling cross-zone load balancing, the ALB provides high availability and fault tolerance for the multi-tier web application.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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AWS Global Accelerator
Why it's wrong here
Global Accelerator directs traffic over the AWS global network to regional endpoints using anycast IP addresses, but it does not balance requests across EC2 instances within a region. It suits improving global latency and failover between regions, not intra-region load distribution across Availability Zones.
- ✓
Application Load Balancer
Why this is correct
An Application Load Balancer operates across multiple Availability Zones, distributing layer 7 requests to healthy EC2 targets in each zone and performing health checks to route around failures. This directly satisfies the multi-AZ high availability constraint for the multi-tier web application.
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AWS Direct Connect
Why it's wrong here
Direct Connect provides a dedicated private network link between on-premises infrastructure and AWS, carrying no traffic distribution function at all. It is the right choice for consistent bandwidth, reduced egress costs and hybrid connectivity, not for spreading incoming requests across EC2 instances.
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Amazon Route 53
Why it's wrong here
Route 53 resolves DNS names and applies routing policies, but it does not distribute individual request traffic across EC2 instances in multiple Availability Zones; that requires a load balancer. Route 53 is correct for domain registration, DNS failover and latency or geolocation-based routing between endpoints.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.