SAA-C03 practice question 9 of 35

A company uses an Amazon EC2 instance to handle requests for a public web application. The application routes traffic to multiple application pages…

Choose your answer, then check it against the explanation and the full breakdown below.

Domain Design High-Performing Architectures

A company uses an Amazon EC2 instance to handle requests for a public web application. The application routes traffic to multiple application pages by using URL paths. The company begins to experience large surges of traffic at unpredictable times. The traffic surges cause the web application to experience issues and to occasionally become unavailable. The company needs to make the web application more scalable to handle sudden increases in traffic. Which solution will meet this requirement?

Answer options

Correct Answer:

Explanation

This solution directly addresses the core requirements of scalability and high availability for a web application. An Application Load Balancer (ALB) is designed to handle HTTP/HTTPS traffic and can perform path-based routing, which matches the application's needs. An Auto Scaling group (ASG) automatically adjusts the number of EC2 instances based on traffic demand, providing the necessary elasticity to handle unpredictable surges. By launching instances from a pre-configured Amazon Machine Image (AMI) and setting a minimum capacity of two, the architecture ensures both consistent application deployment and immediate high availability across multiple instances.

Why Incorrect

B: A Network Load Balancer (NLB) operates at Layer 4 (TCP/UDP) and is not ideal for the application's Layer 7 (HTTP) path-based routing requirement. An ALB is the correct choice.

C: This is a manual, static solution. It does not automatically scale in response to traffic changes and relies on DNS round-robin, which is not a robust method for load balancing or health checking.

D: This solution adds a load balancer and an alarm but fails to add any scaling capability. The single EC2 instance remains the bottleneck, and an alarm only provides notification, not remediation.

References

1. AWS Documentation - What is an Application Load Balancer?: "An Application Load Balancer functions at the application layer

the seventh layer of the Open Systems Interconnection (OSI) model. ... After the load balancer receives a request

it evaluates the listener rules in priority order to determine which rule to apply

and then selects a target from a target group for the rule action. You can configure listener rules to route requests to different target groups based on the content of the application traffic

such as ... path patterns in the URL." This supports the use of an ALB for path-based routing.

Source: AWS Elastic Load Balancing User Guide

"What is an Application Load Balancer?".

2. AWS Documentation - What is Amazon EC2 Auto Scaling?: "Amazon EC2 Auto Scaling helps you ensure that you have the correct number of Amazon EC2 instances available to handle the load for your application. ... You can use dynamic scaling and predictive scaling policies to scale your EC2 capacity in response to changing traffic patterns." This confirms that an Auto Scaling group is the correct service for handling unpredictable traffic surges.

Source: AWS Amazon EC2 Auto Scaling User Guide

"What is Amazon EC2 Auto Scaling?".

3. AWS Well-Architected Framework - Performance Efficiency Pillar: "Use an automated solution to scale your workload based on demand. For example

you can use Auto Scaling to add and remove servers based on a schedule or in response to changing load." This document recommends the exact pattern described in the correct answer for achieving performance efficiency and elasticity.

Source: AWS Well-Architected Framework

Performance Efficiency Pillar whitepaper

PER 4: "How do you select the best performing architecture?"

Section: "Use elasticity to meet demand".

Question 9 of 35

Question breakdown

Tests: Design elastic, highly available web tiers on EC2
Difficulty: Easy

Key idea: An Auto Scaling group behind an Application Load Balancer adds and removes instances automatically while the ALB handles HTTP path routing and health checks.

How to reach the answer

The single instance fails under unpredictable surges, so capacity must scale automatically.
URL path routing indicates a Layer 7 load balancer (ALB).
Bake the current instance into an AMI and launch it from an Auto Scaling group with a minimum of two for availability.
Register the ASG with the ALB target group so new instances receive traffic automatically.

Each option

ACorrect. AMI-based Auto Scaling group behind an ALB scales elastically, supports path routing, and keeps at least two instances healthy.
BIncorrect. Containerizing adds rework, and an NLB works at Layer 4 so it cannot route by URL path.
CIncorrect. Three fixed instances with DNS round-robin do not scale automatically and lack load balancer health checks.
DIncorrect. An ALB in front of one instance plus an alarm only notifies; nothing adds capacity.

Common trap: Option D sounds proactive because it monitors spikes, but an alarm without a scaling action does not add capacity.

In practice: The ALB + Auto Scaling group pattern with target-tracking policies is the default architecture for stateless web applications on EC2.

Remember: Elasticity on EC2 means an Auto Scaling group; Layer 7 routing means an ALB.

Official documentation: What is Amazon EC2 Auto Scaling? · What is an Application Load Balancer?

Drafted with AI assistance and checked against the answer key.

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