The answer is to use an Elastic Network Interface (ENI) with a predefined private IP and attach it to the instance. This approach works because an ENI is a virtual network card that can be created independently of an EC2 instance, allowing you to assign a static private IP address to it and then attach it to any instance in the same Availability Zone. When an instance is terminated, the ENI and its fixed private IP persist in the VPC, enabling you to reattach it to a replacement instance, thereby maintaining a consistent private IP across instance lifecycles. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of how to decouple IP addressing from instance lifecycle management, often appearing in questions about high-availability applications behind Auto Scaling groups. A common trap is confusing Elastic IPs (which are public) or assuming DHCP option sets control IP assignment—neither provides a static private IP per instance. Memory tip: think of an ENI as a "sticky note" for your private IP that survives instance reboots and terminations.
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 is running a critical application on EC2 instances in a VPC. The instances are in an Auto Scaling group across multiple Availability Zones. The application needs to maintain a fixed, private IP address for each instance. Which approach should be used to ensure each instance receives a consistent private IP address?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an Elastic Network Interface (ENI) with a predefined private IP and attach it to the instance
Option D is correct because an Elastic Network Interface (ENI) can be created with a specific private IP and attached to an instance; upon instance termination, the ENI can be reattached to a new instance. Option A is wrong because private IP addresses are assigned at launch and released upon termination. Option B is wrong because Elastic IPs are public IPs. Option C is wrong because DHCP option sets do not assign IP addresses.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 an Elastic Network Interface (ENI) with a predefined private IP and attach it to the instance
Why this is correct
An ENI has a fixed private IP that can be reassigned to another instance if needed.
Related concept
Static NAT maps one inside address to one outside address.
✗
Configure the DHCP option set to assign a static IP
Why it's wrong here
DHCP option sets do not assign IP addresses; they provide configuration like DNS servers.
✗
Assign an Elastic IP to each instance and use that as the private IP
Use a custom AMI that configures a static private IP address via user data
Why it's wrong here
User data runs at boot but cannot guarantee a specific IP if the subnet assigns dynamically.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
Networking and Content Delivery — This question tests Networking and Content Delivery — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use an Elastic Network Interface (ENI) with a predefined private IP and attach it to the instance — Option D is correct because an Elastic Network Interface (ENI) can be created with a specific private IP and attached to an instance; upon instance termination, the ENI can be reattached to a new instance. Option A is wrong because private IP addresses are assigned at launch and released upon termination. Option B is wrong because Elastic IPs are public IPs. Option C is wrong because DHCP option sets do not assign IP addresses.
What should I do if I get this SOA-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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