ANS-C01 Network Implementation Practice Question
A company is deploying a web application in a VPC with an Application Load Balancer (ALB) in front of EC2 instances. The ALB must only accept traffic from the internet and forward it to the instances. Which subnet configuration is correct for the ALB and EC2 instances?
⚠ Common exam trap
It's easy for candidates to assume both the ALB and EC2 instances must be in the same subnet type (both public or both private), failing to recognize that the ALB acts as a reverse proxy that can bridge internet-facing public subnets with backend private subnets.
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
✓
ALB in public subnets, EC2 in private subnets.
An Application Load Balancer (ALB) must be deployed in public subnets to accept traffic directly from the internet, as it requires an internet gateway (IGW) route to receive inbound connections. The EC2 instances should reside in private subnets to enhance security, as they only need to respond to the ALB via the VPC's internal routing, not directly from the internet. This configuration ensures the ALB handles internet-facing traffic while the instances remain isolated from direct external access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ALB in private subnets, EC2 in private subnets with a NAT gateway.
Why it's wrong here
ALB would not receive internet traffic.
- ✓
ALB in public subnets, EC2 in private subnets.
Why this is correct
Standard architecture for internet-facing ALB.
- ✗
ALB in public subnets, EC2 in public subnets.
Why it's wrong here
Backend instances should be private for security.
- ✗
ALB in private subnets, EC2 in public subnets.
Why it's wrong here
ALB needs internet access.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 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 ANS-C01 exam.