The answer is that the Lambda function is not configured with the correct VPC subnet or security group to reach the EC2 instance. This is the likely cause because even when the IAM policy correctly grants ec2:StartInstances on all resources, the Lambda function must have network connectivity to the target EC2 instance; if the function runs outside the instance’s VPC or lacks proper routing and security group rules, the API call will time out or fail silently. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding that IAM permissions alone are insufficient—Lambda’s VPC configuration is a separate, critical requirement for invoking EC2 actions, and the common trap is assuming a valid policy guarantees execution. Remember the memory tip: “Policy permits, but network prohibits”—always check VPC settings before blaming permissions.
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. 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.
An SAP administrator is troubleshooting an issue where an AWS Lambda function is unable to start an EC2 instance. The Lambda execution role has the IAM policy shown in the exhibit. What is the likely cause of the failure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Lambda function is not configured with the correct VPC subnet or security group to reach the EC2 instance.
Option C is correct because the policy allows ec2:StartInstances on all resources, but if the instance is in a different account or region, or if there is a resource policy issue, it may fail. However, the most common issue is that the Lambda function does not have the correct region specified. Option A is wrong because the policy allows s3:GetObject. Option B is wrong because the policy allows ec2:StartInstances. Option D is wrong because the policy allows ec2:DescribeInstances.
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 Lambda function is not configured with the correct VPC subnet or security group to reach the EC2 instance.
Why this is correct
Lambda may need VPC access to start instances in a VPC, but the policy is fine.
The policy explicitly allows ec2:StartInstances on all resources.
✗
The policy does not allow s3:GetObject on the specific backup object.
Why it's wrong here
The policy allows s3:GetObject on any object in the sap-backups bucket.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 PAS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Operations and Maintenance — This question tests Operations and Maintenance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Lambda function is not configured with the correct VPC subnet or security group to reach the EC2 instance. — Option C is correct because the policy allows ec2:StartInstances on all resources, but if the instance is in a different account or region, or if there is a resource policy issue, it may fail. However, the most common issue is that the Lambda function does not have the correct region specified. Option A is wrong because the policy allows s3:GetObject. Option B is wrong because the policy allows ec2:StartInstances. Option D is wrong because the policy allows ec2:DescribeInstances.
What should I do if I get this PAS-C01 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 PAS-C01 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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