The answer is to create an Elastic IP and associate it with the primary network interface of the instance. This works because an Elastic IP (EIP) is a static public IPv4 address that, when attached to an Elastic Network Interface (ENI) in a private subnet, provides a predictable, static private IP address for the instance. The ENI retains the EIP as its primary private IP, ensuring the address persists across instance stops and starts, which is essential for database replication. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of how Elastic IPs and ENIs decouple addressing from instance lifecycle, a common trap being confusion with auto-assign public IP settings or DHCP option sets, which do not affect private IP stability. Remember the key distinction: an Elastic IP is the only AWS service that guarantees a static private IP when attached to an ENI in a private subnet. Memory tip: “EIP on ENI equals static private IP.”
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. 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 has a VPC with an IPv4 CIDR of 10.0.0.0/16. They have a public subnet 10.0.1.0/24 and a private subnet 10.0.2.0/24. They launch an EC2 instance in the private subnet and need it to have a predictable, static private IP address for database replication. Which action should be taken?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an Elastic IP and associate it with the primary network interface of the instance.
Option B is correct because an Elastic IP attached to an ENI in the private subnet provides a static private IP (through the ENI). Option A is wrong because auto-assign public IP does not affect private IP. Option C is wrong because DHCP option set does not assign static IP. Option D is wrong because modifying the subnet does not assign a specific IP to an instance.
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.
✗
Modify the subnet's IP assignment settings to make all IPs static.
Why it's wrong here
Subnets do not have such settings; IP assignment is dynamic by default.
✓
Create an Elastic IP and associate it with the primary network interface of the instance.
Why this is correct
Elastic IP is static and can be associated with an ENI for a fixed private IP.
Use a custom DHCP option set to assign a static IP.
Why it's wrong here
DHCP option sets configure domain name, not IP addresses.
✗
Enable auto-assign public IP on the private subnet.
Why it's wrong here
Does not provide static private IP.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an Elastic IP and associate it with the primary network interface of the instance. — Option B is correct because an Elastic IP attached to an ENI in the private subnet provides a static private IP (through the ENI). Option A is wrong because auto-assign public IP does not affect private IP. Option C is wrong because DHCP option set does not assign static IP. Option D is wrong because modifying the subnet does not assign a specific IP to an instance.
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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Question Discussion
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