ANS-C01 Network Implementation Practice Question
A company is running a web application on EC2 instances behind an Application Load Balancer (ALB) in a VPC. The application needs to store session state in an ElastiCache Redis cluster. The Redis cluster should not be accessible from the internet. Which network design should be used?
⚠ Common exam trap
Many exam-takers think a NAT Gateway is required for EC2 instances in private subnets to communicate with ElastiCache, but in reality, VPC internal traffic uses private IPs and does not require a NAT Gateway, which is only for outbound internet access.
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
✓
Place both the EC2 instances and the Redis cluster in private subnets with appropriate security groups.
Placing both the EC2 instances and the ElastiCache Redis cluster in private subnets ensures that the Redis cluster is not accessible from the internet, meeting the security requirement. The EC2 instances can communicate with the Redis cluster within the same VPC using private IP addresses, and security groups can be used to restrict traffic to only the necessary ports (e.g., TCP 6379 for Redis) from the EC2 instances' security group. This design avoids exposing the Redis cluster to any public network, aligning with best practices for internal caching layers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place the Redis cluster in a public subnet and restrict access via security group.
Why it's wrong here
Public subnet implies internet exposure, even with security groups.
- ✗
Place the Redis cluster in a private subnet and the EC2 instances in a private subnet, with a NAT Gateway for outbound traffic.
Why it's wrong here
NAT Gateway is for internet access, not needed for VPC internal communication.
- ✗
Place the Redis cluster in a private subnet and the EC2 instances in a public subnet.
Why it's wrong here
EC2 instances should be in private subnets for security.
- ✓
Place both the EC2 instances and the Redis cluster in private subnets with appropriate security groups.
Why this is correct
Both in private subnets, security groups allow traffic from EC2 to Redis.
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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.