Multi-Tier Application Network Segmentation with Security Groups

A cloud architect is designing a multi-tier application in a public cloud. The web tier must be accessible from the internet, while the application and database tiers must only be reachable from the web tier. The architect needs to ensure that even if the web server is compromised, the attacker cannot directly access the database. Which architecture BEST meets this requirement?

Quick Answer

The correct architecture places the web tier in a public subnet with a security group allowing HTTP/HTTPS from 0.0.0.0/0, and the app and database tiers in private subnets with security groups that only permit traffic from the web tier’s security group. This implements defense-in-depth by enforcing multi-tier application network segmentation, ensuring that even if the web server is compromised, the attacker cannot directly reach the database because the database security group explicitly denies traffic from any source other than the web tier’s security group, and the private subnets lack a direct internet route. On the Certified Cloud Security Professional CCSP exam, this scenario tests your understanding of how security groups act as stateful, host-level firewalls to enforce least-privilege segmentation between tiers, a core concept in cloud network security. A common trap is assuming that placing all tiers in private subnets is sufficient, but the key is referencing the web tier’s security group as the source, not just the subnet CIDR. Memory tip: think “public web, private app, group-to-group only” to avoid direct IP-based rules.

⚠ Common exam trap

Watch out — candidates often confuse network ACLs (stateless, IP-based) with security groups (stateful, can reference other security groups), leading them to choose Option B because they think ACLs provide sufficient segmentation, but they overlook the need for group-based source references to prevent lateral movement from a compromised host.

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 the web tier in a public subnet with a security group allowing HTTP/HTTPS from 0.0.0.0/0, and place the app and database tiers in private subnets with security groups allowing traffic only from the web tier's security group.

It implements defense-in-depth by placing the web tier in a public subnet with a security group that allows inbound HTTP/HTTPS from the internet, while the app and database tiers reside in private subnets with security groups that only permit traffic from the web tier's security group. This ensures that even if the web server is compromised, the attacker cannot directly reach the database because the database security group explicitly denies traffic from any source other than the web tier's security group, and the private subnets have no direct internet route.

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 all tiers in the same subnet and use a single security group to control inbound traffic.
Why it's wrong here
This allows direct access between tiers if the security group allows it, compromising isolation.
✗
Place all tiers in the same VPC but different subnets, and use network ACLs to restrict traffic.
Why it's wrong here
Network ACLs are stateless and less granular; security groups are preferred for instance-level control.
✓
Place the web tier in a public subnet with a security group allowing HTTP/HTTPS from 0.0.0.0/0, and place the app and database tiers in private subnets with security groups allowing traffic only from the web tier's security group.
Why this is correct
This provides proper isolation: private subnets with security group references restrict access to the web tier only.
✗
Use a VPN to connect the tiers and rely on IPsec policies for segmentation.
Why it's wrong here
VPNs provide encrypted tunnels but are not designed for internal segmentation.

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Same concept, more angles

1 more way this is tested on CCSP

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A financial services company is migrating its on-premises data center to a public cloud IaaS environment. During the transition, the security team must ensure that the same network segmentation and firewall rules are maintained. Which of the following is the BEST approach to replicate the on-premises network security controls in the cloud?

easy

A.Configure a site-to-site VPN between on-premises and cloud to extend the existing network.
✓ B.Use virtual private clouds (VPCs) with subnets and security groups to enforce segmentation and firewall rules.
C.Implement an intrusion detection and prevention system (IDPS) to monitor traffic.
D.Deploy a software-defined WAN (SD-WAN) to manage network traffic between cloud resources.

Why B: VPCs with subnets and security groups provide native, software-defined network segmentation and stateful firewall rules that directly replicate on-premises network segmentation and ACLs. Security groups act as virtual firewalls at the instance level, while network ACLs provide subnet-level stateless filtering, together enabling granular control without extending the on-premises network.

Last reviewed: Jun 11, 2026

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