The answer is that the user is not specifying the subnet ID when launching the instance. The `ec2:Subnet` condition key evaluates the subnet specified in the `RunInstances` API call, so if the user launches an instance without explicitly providing a subnet ID—for example, by relying on the default VPC’s automatic subnet selection—the condition check fails, and the action is denied. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of how condition keys interact with API parameters; a common trap is assuming the condition key applies globally to all subnets, but it only works when the subnet is passed in the request. Remember that `ec2:Subnet` is a request-based condition key, not a resource-based one, meaning the user must explicitly include the subnet ID in their launch command. Memory tip: “Specify to satisfy”—if the policy demands a specific subnet, you must specify it in the launch request.
SOA-C02 Security and Compliance Practice Question
This SOA-C02 practice question tests your understanding of security and compliance. 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 SysOps administrator is troubleshooting an issue where an IAM user is unable to launch an EC2 instance in a specific subnet. The user has the following IAM policy:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The user is not specifying the subnet ID when launching the instance.
Option B is correct because the 'ec2:Subnet' condition key requires the user to specify the subnet ID in the RunInstances call. If the user does not specify a subnet (e.g., using the default VPC), the condition fails. Option A is wrong because the policy allows RunInstances, not just Describe. Option C is wrong because the condition is explicitly for subnet-12345, so it does not deny all subnets. Option D is wrong because the condition key 'ec2:Subnet' is valid for RunInstances.
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 policy does not allow the 'ec2:DescribeSubnets' action, so the user cannot list subnets.
Why it's wrong here
The error is about launching, not describing.
✓
The user is not specifying the subnet ID when launching the instance.
Why this is correct
The condition requires the subnet ID to be provided.
The policy denies all subnets except subnet-12345.
Why it's wrong here
The policy allows only that subnet, but the user may be using a different subnet.
✗
The condition key 'ec2:Subnet' is not supported for RunInstances.
Why it's wrong here
It is supported.
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.
Security and Compliance — This question tests Security and Compliance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The user is not specifying the subnet ID when launching the instance. — Option B is correct because the 'ec2:Subnet' condition key requires the user to specify the subnet ID in the RunInstances call. If the user does not specify a subnet (e.g., using the default VPC), the condition fails. Option A is wrong because the policy allows RunInstances, not just Describe. Option C is wrong because the condition is explicitly for subnet-12345, so it does not deny all subnets. Option D is wrong because the condition key 'ec2:Subnet' is valid for RunInstances.
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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