TF-003 Use the core Terraform workflow Practice Question
This TF-003 practice question tests your understanding of use the core terraform workflow. 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 developer is troubleshooting a Terraform configuration that fails during `terraform plan` with the error: "Error: Invalid reference". The error points to a line that references `var.environment` in a module block. 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.
The Terraform version does not support module variables
Why wrong: Module variables have been supported since early versions.
B
The variable `var.environment` is not defined in the root module's variables.tf
Why wrong: The root module uses `var.environment` in a module block, so it should be defined in root. But the error is about the module block, not the root's definition.
C
The variable `environment` is not defined in the child module's variables.tf
Correct! When referencing `var.environment` inside a module block, that variable must be declared in the child module.
D
The module source path is invalid
Why wrong: Invalid source would give a different error.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The variable `environment` is not defined in the child module's variables.tf
Option C is correct because when a Terraform module block references a variable like `var.environment`, that variable must be defined in the child module's `variables.tf` file. The error 'Invalid reference' indicates Terraform cannot resolve the variable within the module's scope, meaning the child module does not declare an input variable named `environment`. Without this declaration, the module cannot accept the value passed from the root module.
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 Terraform version does not support module variables
Why it's wrong here
Module variables have been supported since early versions.
✗
The variable `var.environment` is not defined in the root module's variables.tf
Why it's wrong here
The root module uses `var.environment` in a module block, so it should be defined in root. But the error is about the module block, not the root's definition.
✓
The variable `environment` is not defined in the child module's variables.tf
Why this is correct
Correct! When referencing `var.environment` inside a module block, that variable must be declared in the child module.
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 module source path is invalid
Why it's wrong here
Invalid source would give a different error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
HashiCorp often tests the distinction between root module variables and child module input variables, trapping candidates who assume `var.environment` must be defined in the root module's `variables.tf` rather than in the child module's `variables.tf`.
Detailed technical explanation
How to think about this question
In Terraform, each module has its own variable namespace; variables must be explicitly declared in the child module's `variables.tf` using the `variable` block. The root module passes values via `module` block arguments, but the child module must define those input variables. A common subtlety is that if the variable is defined but with a different name or type, Terraform will produce a type mismatch error rather than an 'Invalid reference' error. Real-world scenarios often involve forgetting to add a new variable to the child module after adding it to the root module's configuration.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Use the core Terraform workflow — This question tests Use the core Terraform workflow — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The variable `environment` is not defined in the child module's variables.tf — Option C is correct because when a Terraform module block references a variable like `var.environment`, that variable must be defined in the child module's `variables.tf` file. The error 'Invalid reference' indicates Terraform cannot resolve the variable within the module's scope, meaning the child module does not declare an input variable named `environment`. Without this declaration, the module cannot accept the value passed from the root module.
What should I do if I get this TF-003 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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Question Discussion
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