The correct answer is to add a VPC Gateway Endpoint for S3 and update the route table, because an EC2 instance in a private subnet cannot reach S3 through a NAT Gateway or Internet Gateway without a direct route. A VPC Gateway Endpoint uses a prefix list in the route table to route traffic destined for S3 over the AWS network, bypassing the need for internet access entirely; without this endpoint, the private subnet has no path to S3, causing HTTPS requests to time out even if security groups and network ACLs allow outbound traffic. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of how Gateway Endpoints differ from Interface Endpoints and why S3 specifically requires a route table update rather than a DNS change or IAM role. A common trap is assuming a NAT Gateway or Internet Gateway is needed for private subnet egress, but S3’s prefix list makes the Gateway Endpoint the only viable solution. Memory tip: S3 is a bucket, not a tunnel—use a Gateway Endpoint to keep traffic on the highway, not the internet.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 security engineer is troubleshooting connectivity issues from an EC2 instance in a private subnet to an S3 bucket. The instance has a security group allowing outbound HTTPS (443) to 0.0.0.0/0, and the subnet's network ACL allows outbound HTTPS to 0.0.0.0/0. However, requests to S3 are timing out. Which additional configuration is most likely required?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a VPC Gateway Endpoint for S3 and update the route table
Option C is correct because S3 endpoints are accessed via a prefix list in route tables; without a VPC Gateway Endpoint for S3, traffic goes through a NAT Gateway or Internet Gateway, but the private subnet lacks a route to the internet. Option A is wrong because S3 supports HTTPS without TLS termination. Option B is wrong because S3 is a global service and does not require a specific region endpoint configuration at the VPC level. Option D is wrong because S3 does not require an IAM role for connectivity; that is for access permissions.
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.
✗
Attach an IAM role to the EC2 instance with S3 permissions
Why it's wrong here
IAM role provides access permissions, not network connectivity.
✗
Modify the security group to allow traffic to the S3 region-specific IP range
Why it's wrong here
Security group egress to 0.0.0.0/0 already allows all outbound HTTPS.
✓
Add a VPC Gateway Endpoint for S3 and update the route table
Why this is correct
A Gateway Endpoint provides a route to S3 without internet access.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
S3 supports HTTPS natively; TLS termination is not needed.
Common exam traps
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Add a VPC Gateway Endpoint for S3 and update the route table — Option C is correct because S3 endpoints are accessed via a prefix list in route tables; without a VPC Gateway Endpoint for S3, traffic goes through a NAT Gateway or Internet Gateway, but the private subnet lacks a route to the internet. Option A is wrong because S3 supports HTTPS without TLS termination. Option B is wrong because S3 is a global service and does not require a specific region endpoint configuration at the VPC level. Option D is wrong because S3 does not require an IAM role for connectivity; that is for access permissions.
What should I do if I get this SCS-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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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