The answer is to ensure instances communicate using private IP addresses within the same VPC. This is correct because traffic between EC2 instances in the same AWS Region and VPC that uses private IP addresses stays entirely within the AWS network backbone, incurring no data transfer costs, whereas traffic routed over public or Elastic IP addresses is charged at standard internet data transfer rates. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this concept tests your understanding of cost optimization through network architecture, and a common trap is assuming that using a NAT Gateway or VPC endpoint for instance-to-instance traffic reduces costs—in reality, both add charges. A reliable memory tip is “private IPs are free, public IPs cost fees,” reminding you that for intra-region, intra-VPC communication, always default to private addressing to minimize expenses.
SOA-C02 Cost and Performance Optimization Practice Question
This SOA-C02 practice question tests your understanding of cost and performance optimization. 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 wants to reduce data transfer costs for traffic between EC2 instances in the same AWS Region. Which action should the SysOps administrator take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ensure instances communicate using private IP addresses within the same VPC
Option D is correct because using private IP addresses avoids data transfer charges over the internet. Public IPs incur costs. VPC endpoints are for accessing AWS services, not for instance-to-instance traffic. NATGateway adds cost. Direct Connect is for on-premises connectivity and is expensive.
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.
Use VPC endpoints to communicate between instances
Why it's wrong here
VPC endpoints are for accessing AWS services, not instance-to-instance.
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.
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.
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: Ensure instances communicate using private IP addresses within the same VPC — Option D is correct because using private IP addresses avoids data transfer charges over the internet. Public IPs incur costs. VPC endpoints are for accessing AWS services, not for instance-to-instance traffic. NAT Gateway adds cost. Direct Connect is for on-premises connectivity and is expensive.
What should I do if I get this SOA-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 SOA-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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This SOA-C02 practice question is part of Courseiva's free Amazon Web Services 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 SOA-C02 exam.
Question Discussion
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