The answer is that the most likely cause is the AWS region lacks a default VPC or the VPC ID was not specified. This is correct because when Terraform apply fails with a subnet VPC internet gateway missing error, it indicates the subnet’s target VPC has no internet gateway attached, which is essential for public subnet internet access. On the Project Management Professional PMP exam, this scenario tests your ability to diagnose infrastructure provisioning failures by linking cloud networking fundamentals to project risk management—a common trap is assuming all AWS regions automatically include a default VPC with an internet gateway, but newer regions or custom VPCs often omit it. Remember the memory tip: “No gateway, no getaway”—if the internet gateway is missing, your instances cannot reach the internet, and Terraform will halt the apply.
PMP Process — Managing Technical Aspects Practice Question
This PMP practice question tests your understanding of process — managing technical aspects. 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.
Exhibit
Refer to the exhibit.
```
Error: Terraform apply failed
Error: Error creating EC2 Instance: VPCIdNotSpecified: No default VPC found
status code: 400, request id: ...
on main.tf line 10, in resource "aws_instance" "web":
10: resource "aws_instance" "web" {
```
Refer to the exhibit. A project team is using Terraform to provision infrastructure. The apply failed with the shown error. 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.
Refer to the exhibit.
```
Error: Terraform apply failed
Error: Error creating EC2 Instance: VPCIdNotSpecified: No default VPC found
status code: 400, request id: ...
on main.tf line 10, in resource "aws_instance" "web":
10: resource "aws_instance" "web" {
```
A
The instance type is not supported in the region.
Why wrong: The error is about VPC, not instance type.
B
The AWS region does not have a default VPC, or the VPC ID is not specified.
The error message indicates the default VPC is missing, and no VPC ID was provided.
C
The AWS credentials are invalid.
Why wrong: The error is about VPC, not authentication.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The AWS region does not have a default VPC, or the VPC ID is not specified.
The error message indicates that the subnet's VPC does not have an internet gateway attached, which is required for instances launched in a public subnet to communicate with the internet. Option B is correct because the default VPC typically has an internet gateway, but if it's missing or the VPC ID is not specified, Terraform cannot associate the subnet with a valid VPC, causing the apply to fail.
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 instance type is not supported in the region.
Why it's wrong here
The error is about VPC, not instance type.
✓
The AWS region does not have a default VPC, or the VPC ID is not specified.
Why this is correct
The error message indicates the default VPC is missing, and no VPC ID was provided.
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 AWS credentials are invalid.
Why it's wrong here
The error is about VPC, not authentication.
✗
The AMI ID specified is incorrect.
Why it's wrong here
The error does not mention AMI.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the error is about invalid credentials or AMI ID, but the specific subnet/VPC error message points directly to a missing internet gateway or VPC configuration issue.
Detailed technical explanation
How to think about this question
When launching an EC2 instance in a public subnet, Terraform requires either a default VPC with an internet gateway or an explicitly specified VPC ID with an attached internet gateway. The error 'VPCIdNotSpecified' occurs when the subnet is not associated with a VPC that has an internet gateway, which is a common misconfiguration when using non-default VPCs without proper gateway setup. In real-world scenarios, this often happens when teams delete the default VPC or create custom VPCs without attaching an internet gateway.
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.
TExam Day Tips
→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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PMP question in full detail.
Process — Managing Technical Aspects — This question tests Process — Managing Technical Aspects — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The AWS region does not have a default VPC, or the VPC ID is not specified. — The error message indicates that the subnet's VPC does not have an internet gateway attached, which is required for instances launched in a public subnet to communicate with the internet. Option B is correct because the default VPC typically has an internet gateway, but if it's missing or the VPC ID is not specified, Terraform cannot associate the subnet with a valid VPC, causing the apply to fail.
What should I do if I get this PMP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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