The correct answer involves setting the RDS instance's 'Publicly accessible' option to 'No', placing the web tier instances in a private subnet, and configuring the database security group to allow inbound traffic only from the web tier security group. This layered approach ensures that the database is never assigned a public IP address, the web servers themselves are not directly reachable from the internet, and connectivity is restricted to a specific port exclusively from the web tier's security group, creating a tightly controlled network path. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of defense-in-depth for multi-tier architectures, often appearing as a "choose three" question where a common trap is selecting a public subnet for the database or confusing Parameter Store for network access control. Remember the three-layer mantra: private subnet for compute, security group referencing for traffic, and no public endpoint for the database—think "subnet, group, disable public" to lock down your data tier.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is designing a new multi-tier web application on AWS. The application uses an Auto Scaling group of EC2 instances for the web tier and an Amazon RDS for PostgreSQL DB instance for the database. To improve security, the company wants to ensure that the web tier instances can connect to the database only through a specific port and that the database is not accessible from the internet. Which steps should the company take? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the database security group to allow inbound traffic on port 5432 from the web tier security group.
Options A, B, and D are correct. Placing web tier instances in a private subnet (A) ensures they are not internet-facing. Using a security group for the database that allows inbound traffic only from the web tier security group (B) restricts access. Enabling the 'publicly accessible' flag to 'No' (D) ensures no public endpoint. Option C is wrong because placing the database in a public subnet would expose it. Option E is wrong because storing secrets in Parameter Store is for credentials, not network access.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Launch the database instance in a public subnet.
Why it's wrong here
Public subnets are internet-facing; database should be in private subnet.
✓
Configure the database security group to allow inbound traffic on port 5432 from the web tier security group.
Why this is correct
Security group rules restrict traffic to only the web tier.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Design for New Solutions — This question tests Design for New Solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure the database security group to allow inbound traffic on port 5432 from the web tier security group. — Options A, B, and D are correct. Placing web tier instances in a private subnet (A) ensures they are not internet-facing. Using a security group for the database that allows inbound traffic only from the web tier security group (B) restricts access. Enabling the 'publicly accessible' flag to 'No' (D) ensures no public endpoint. Option C is wrong because placing the database in a public subnet would expose it. Option E is wrong because storing secrets in Parameter Store is for credentials, not network access.
What should I do if I get this SAP-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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