ANS-C01 Network Implementation Practice Question
A company is designing a multi-tier application with web servers in public subnets and database servers in private subnets. The database servers should only be accessible from the web servers. Which AWS feature should be used to enforce this?
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
✓
Security groups that reference the web server security group as a source
Security groups are stateful and act as a virtual firewall for individual instances. By referencing the web server security group as a source in the database security group's inbound rules, you allow traffic only from instances in that security group. This provides granular control at the instance level. Option B is incorrect because VPC endpoints are used to privately connect to AWS services, not to restrict database access. Options C and D are incorrect because network ACLs are stateless and applied at the subnet level, not at the instance level, and they require explicit allow rules for return traffic. Using a NACL with allow rules for the web server subnet CIDR would still allow any instance in that subnet, not just the web servers, and would require managing ephemeral ports.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Security groups that reference the web server security group as a source
Why this is correct
Security groups allow you to specify another security group as the source, enabling fine-grained access control.
- ✗
VPC endpoints to restrict access to the database servers
Why it's wrong here
VPC endpoints are for accessing AWS services, not for controlling traffic between instances.
- ✗
Network ACLs with allow rules for the web server subnet CIDR
Why it's wrong here
NACLs are stateless and require both inbound and outbound rules; they also apply to all instances in the subnet, not just the database servers.
- ✗
Network ACLs with deny rules for all traffic except from the web server subnet
Why it's wrong here
NACLs are stateless and less secure than security groups for this purpose.
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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.