← SOA-C02·Amazon Web Services

Question 958 of 1,546

Cost and Performance Optimization →hardMultiple ChoiceObjective-mapped

SOA-C02 Cost and Performance Optimization Practice Question

This SOA-C02 practice question tests your understanding of cost and performance optimization. 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 SysOps administrator is troubleshooting a cost overrun in an AWS account. The cost explorer shows that data transfer costs have significantly increased. The architecture includes an Application Load Balancer (ALB) internet-facing, EC2 instances in private subnets, and an S3 bucket for static assets. Which action will MOST effectively reduce data transfer costs?

A
Enable Amazon CloudFront to cache static assets and reduce direct requests to the ALB.
Why wrong: CloudFront reduces data transfer from origin but does not reduce ALB-to-EC2 costs.
B
Implement a VPC Gateway Endpoint for S3 so that traffic from EC2 to S3 stays within the AWS network.
Gateway endpoints are free and reduce data transfer costs to S3.
C
Replace the NAT Gateway with a NAT instance to reduce hourly charges.
Why wrong: NAT Gateway data transfer costs are separate; this does not address ALB/EC2 costs.
D
Change the ALB to internal (private) and use AWS Direct Connect for user access.
Why wrong: This adds complexity and cost of Direct Connect.

Full breakdown with real-world context →

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

✓

Implement a VPC Gateway Endpoint for S3 so that traffic from EC2 to S3 stays within the AWS network.

The correct answer is B. A VPC Gateway Endpoint for S3 allows EC2 instances in private subnets to access S3 without traversing the internet or a NAT gateway, eliminating data transfer costs for S3 traffic. Option A is incorrect because CloudFront reduces latency and offloads requests from the ALB, but data transfer from ALB to EC2 still incurs costs. Option C is incorrect because NAT Gateway charges are for data processing and transfer, and replacing it with a NAT instance may reduce hourly charges but does not address data transfer costs to S3. Option D is incorrect because making the ALB internal prevents direct internet access, requiring a VPN or Direct Connect, which adds costs.

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.

✗
Enable Amazon CloudFront to cache static assets and reduce direct requests to the ALB.
Why it's wrong here
CloudFront reduces data transfer from origin but does not reduce ALB-to-EC2 costs.
✓
Implement a VPC Gateway Endpoint for S3 so that traffic from EC2 to S3 stays within the AWS network.
Why this is correct
Gateway endpoints are free and reduce data transfer costs to S3.
Related concept
CIDR notation defines the prefix length.
✗
Replace the NAT Gateway with a NAT instance to reduce hourly charges.
Why it's wrong here
NAT Gateway data transfer costs are separate; this does not address ALB/EC2 costs.
✗
Change the ALB to internal (private) and use AWS Direct Connect for user access.
Why it's wrong here
This adds complexity and cost of Direct Connect.

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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.

Visual reference

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

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 SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Cost and Performance Optimization — This question tests Cost and Performance Optimization — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Implement a VPC Gateway Endpoint for S3 so that traffic from EC2 to S3 stays within the AWS network. — The correct answer is B. A VPC Gateway Endpoint for S3 allows EC2 instances in private subnets to access S3 without traversing the internet or a NAT gateway, eliminating data transfer costs for S3 traffic. Option A is incorrect because CloudFront reduces latency and offloads requests from the ALB, but data transfer from ALB to EC2 still incurs costs. Option C is incorrect because NAT Gateway charges are for data processing and transfer, and replacing it with a NAT instance may reduce hourly charges but does not address data transfer costs to S3. Option D is incorrect because making the ALB internal prevents direct internet access, requiring a VPN or Direct Connect, which adds costs.

What should I do if I get this SOA-C02 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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