The answer is that the Lambda execution role is missing the ec2:CreateNetworkInterface permission. This is the likely cause because when a Lambda function is configured to run inside a VPC, AWS Lambda must create an elastic network interface (ENI) in your VPC on your behalf to enable connectivity to resources like RDS or ElastiCache. Without the explicit ec2:CreateNetworkInterface permission in the IAM role attached to the function, CloudFormation cannot provision the ENI, resulting in the stack creation failure. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of Lambda’s VPC networking requirements versus common misconfigurations—many candidates mistakenly focus on the VPC’s route tables or security groups, but the error message directly points to an IAM permissions gap. A useful memory tip is to think “Lambda needs ENI creation rights” and remember that the ec2:CreateNetworkInterface action is a required permission for any Lambda function deployed in a VPC.
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. 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 company uses AWS CloudFormation to create a stack with a Lambda function that uses a VPC. The stack creation fails with 'CREATE_FAILED: The provided execution role does not have permissions to call ec2:CreateNetworkInterface on the resource'. What is the likely cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Lambda execution role is missing the ec2:CreateNetworkInterface permission.
Option C is correct: Lambda needs permissions to create elastic network interfaces. Option A is not related. Option B is not required. Option D is not the cause.
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.
✗
The VPC does not have a subnet with internet access.
Why it's wrong here
Lambda can work in private subnets with VPC endpoints; the error is about permissions.
✗
The CloudFormation template does not specify a security group.
Why it's wrong here
Missing security group would cause a different error.
✗
The Lambda function code has a syntax error.
Why it's wrong here
Syntax errors cause invocation failures but not stack creation failures.
✓
The Lambda execution role is missing the ec2:CreateNetworkInterface permission.
Why this is correct
Lambda needs ec2:CreateNetworkInterface, ec2:DescribeNetworkInterfaces, and ec2:DeleteNetworkInterface to manage VPC networking.
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.
SDLC Automation — This question tests SDLC Automation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Lambda execution role is missing the ec2:CreateNetworkInterface permission. — Option C is correct: Lambda needs permissions to create elastic network interfaces. Option A is not related. Option B is not required. Option D is not the cause.
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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Question Discussion
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