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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
A single security group spanning one subnet cannot enforce tier-to-tier separation: any rule permitting web-to-database traffic also permits a compromised web host to reach the database directly, since no subnet boundary or per-tier rule set exists. Security groups suit controlling traffic to individual instances, not isolating tiers.
- ✗
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 subnet-level filters evaluated before security groups; they cannot reference security group members, so permitting the web tier's ephemeral return ports also exposes the database to any host in that subnet range. NACLs suit coarse subnet boundary control, not identity-based tier isolation.
- ✓
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
Security-group referencing means the database accepts traffic only from instances carrying the web tier's group identity, not from any IP in the subnet. A compromised web server therefore cannot pivot directly to the database, satisfying the lateral-movement constraint.
- ✗
Use a VPN to connect the tiers and rely on IPsec policies for segmentation.
Why it's wrong here
IPsec policies encrypt and authenticate traffic between VPN endpoints, but a compromised web server already holds valid tunnel credentials, so it can still reach the database. VPNs suit securing traffic over untrusted networks, not enforcing application-tier reachability boundaries within one cloud environment.
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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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CCSP practice question is part of Courseiva's free ISC2 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 CCSP exam.