The answer is that the security group must be specified by GroupId, not by name, when launching an EC2 instance into a VPC. This is because in a VPC, security groups are identified by their unique ID (e.g., sg-12345), whereas the name-based reference only works in EC2-Classic, which AWS has largely phased out. The CloudFormation template likely used the name "default" for the security group, but since the instance is launched in a VPC, CloudFormation cannot resolve that name to a valid group, causing the "does not exist" error. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of the critical distinction between VPC and EC2-Classic resource referencing—a common trap where candidates assume a security group name works everywhere. Remember, in a VPC, always use the GroupId, not the GroupName. A simple memory tip: "In VPC, ID is key; names are for the old EC2-Classic sea."
SOA-C02 Deployment, Provisioning, and Automation Practice Question
This SOA-C02 practice question tests your understanding of deployment, provisioning, and 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.
Refer to the exhibit. A SysOps administrator creates this CloudFormation template. The stack creation fails with the error: 'The security group 'default' does not exist'. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The instance is launched in a VPC, but the security group is specified by name instead of group ID.
The correct answer is B because the default security group exists in a VPC, but the EC2 instance is launched in EC2-Classic (default) which uses the 'default' security group name. However, if the instance is launched in a VPC, the security group must be specified by GroupId, not by name. The template uses a name, which is only valid for EC2-Classic. Since most AWS accounts now use VPC, the security group name 'default' is not recognized. Option A is incorrect because the VPC does have a default security group, but it's identified by ID. Option C is incorrect because the default group exists. Option D is incorrect because the instance is launched in the default VPC, but the security group reference is incorrect.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 default security group.
Why it's wrong here
The default VPC always has a default security group.
✗
The instance is launched in EC2-Classic, which does not support security groups.
Why it's wrong here
EC2-Classic does support security groups by name.
✓
The instance is launched in a VPC, but the security group is specified by name instead of group ID.
Why this is correct
In a VPC, security groups are referenced by ID, not name.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'default' security group is not present in the account.
Why it's wrong here
The default security group is present in every VPC.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which SOA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Deployment, Provisioning, and Automation — This question tests Deployment, Provisioning, and Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The instance is launched in a VPC, but the security group is specified by name instead of group ID. — The correct answer is B because the default security group exists in a VPC, but the EC2 instance is launched in EC2-Classic (default) which uses the 'default' security group name. However, if the instance is launched in a VPC, the security group must be specified by GroupId, not by name. The template uses a name, which is only valid for EC2-Classic. Since most AWS accounts now use VPC, the security group name 'default' is not recognized. Option A is incorrect because the VPC does have a default security group, but it's identified by ID. Option C is incorrect because the default group exists. Option D is incorrect because the instance is launched in the default VPC, but the security group reference is incorrect.
What should I do if I get this SOA-C02 question wrong?
Identify which SOA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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