The answer is MapPublicIpOnLaunch, which must be set to true on the subnet resource in the CloudFormation template. This property directly controls whether any EC2 instance launched in that subnet automatically receives a public IPv4 address from Amazon’s public IP pool, making it essential for public subnets that need direct internet access. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this concept tests your understanding of subnet-level versus instance-level networking attributes, and a common trap is confusing MapPublicIpOnLaunch with the instance-level AssociatePublicIpAddress parameter, which is used during launch but is not a subnet property. Remember that DNS-related options like EnableDnsHostnames and EnableDnsSupport are VPC-wide settings that do not assign public IPs. A simple memory tip: think “Map the subnet to public IPs on launch” — the word “Map” in the property name signals it’s a subnet-level mapping, not an instance-level association.
DOP-C02 Configuration Management and IaC Practice Question
This DOP-C02 practice question tests your understanding of configuration management and iac. 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 DevOps engineer is using AWS CloudFormation to deploy a stack that includes a VPC with public and private subnets. The engineer wants to ensure that the public subnets automatically get a public IP address assigned to instances launched in them. Which property should be set?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
MapPublicIpOnLaunch on the subnet
Option D is correct because MapPublicIpOnLaunch set to true allows public IP assignment. Option A (AssociatePublicIpAddress) is not a subnet property. Option B (EnableDnsHostnames) is for VPC DNS. Option C (EnableDnsSupport) is also for VPC DNS.
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.
EnableDnsHostnames allows DNS hostnames, not public IP assignment.
✗
AssociatePublicIpAddress on the instance
Why it's wrong here
AssociatePublicIpAddress is an instance-level property, but the question asks for subnet-level.
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Configuration Management and IaC — This question tests Configuration Management and IaC — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: MapPublicIpOnLaunch on the subnet — Option D is correct because MapPublicIpOnLaunch set to true allows public IP assignment. Option A (AssociatePublicIpAddress) is not a subnet property. Option B (EnableDnsHostnames) is for VPC DNS. Option C (EnableDnsSupport) is also for VPC DNS.
What should I do if I get this DOP-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 DOP-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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