CCSP Cloud Platform and Infrastructure Security Practice Question
A security architect is designing a VPC for a three-tier web application. Which of the following VPC subnet designs provides the most secure isolation for the database tier?
⚠ Common exam trap
CCSP often tests the misconception that VPC peering or public subnets with tight security groups provide equivalent isolation, when subnet-level private placement plus SG chaining is the canonical secure design.
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
✓
Database tier in a private subnet with security group allowing only the application tier
Placing the database tier in a private subnet with a security group that only allows traffic from the application tier's security group enforces both network-layer isolation (no route to the internet) and identity-based access control (SG-to-SG referencing). This is the AWS-recommended pattern for three-tier architectures because it minimizes the attack surface and prevents lateral movement from compromised web-tier instances. The database has no public IP and no route to an internet gateway, so it cannot be reached directly from outside the VPC.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Database tier in a private subnet with security group allowing only the application tier
Why this is correct
Placing the database tier in a private subnet removes any route to the internet, and a security group permitting only the application tier enforces least-privilege, tier-to-tier access. This satisfies the isolation requirement by ensuring no other subnet or external source can reach the database.
- ✗
Database tier in a separate VPC with VPC peering
Why it's wrong here
VPC peering facilitates network connectivity between two distinct VPCs, but it fails to provide the required isolation for a three-tier application because it allows routing between subnets within the same logical network boundary. This design is intended for connecting disparate workloads or third-party environments that require private IP communication. It becomes the correct choice when integrating independent production environments rather than segmenting layers of a single application architecture.
- ✗
Database tier in a public subnet with security group allowing only the application tier
Why it's wrong here
Placing the database tier in a public subnet exposes it to internet routing regardless of security group rules, so isolation depends on a single stateful filter rather than network-layer separation. Private subnets with no route to an internet gateway are the correct design; public subnets suit internet-facing load balancers and bastion hosts.
- ✗
Database tier in the same subnet as the application tier
Why it's wrong here
Placing the database in the application subnet removes the subnet boundary, so any application-tier compromise or misconfigured security group exposes the database directly. Shared subnets suit tightly coupled components; isolation for a database tier requires its own private subnet with security groups referencing the application tier.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
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