TF-004 Interact with Terraform modules Practice Question
A developer wants to create multiple instances of a module that provisions a single EC2 instance. They want to create 3 EC2 instances. Which approach is most efficient and concise?
⚠ Common exam trap
In the Terraform Associate exam, candidates are often tested on understanding that `count` is the most concise and efficient way to create a fixed number of identical module instances, while `for_each` is better for creating instances from a set of distinct keys or when you need to manage each instance independently with a unique identifier.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the 'count' meta-argument in the module block.
The `count` meta-argument in a module block allows you to create multiple instances of the entire module (including its EC2 instance) by specifying a number. This is the most efficient and concise approach when you need a fixed number of identical module instances, as it avoids code duplication and leverages Terraform's built-in iteration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the source argument to a list of three URLs.
Why it's wrong here
The `source` argument within a module block is designed to accept a single string value, which specifies the path or URL to the module's source code. Terraform expects this argument to point to a singular location for module definition, indicating *what* module to use, not *how many* instances to create. Providing a list of three URLs would result in a configuration parsing error, as it fundamentally misinterprets the argument's purpose.
- ✓
Use the 'count' meta-argument in the module block.
Why this is correct
The `count` meta-argument is specifically designed to create multiple identical instances of a resource or module block. By setting `count` to an integer value, such as `3`, Terraform will instantiate the module three times, creating separate, distinct instances. This method is highly efficient and concise for provisioning a fixed number of similar components, as it avoids repetition and leverages Terraform's built-in lifecycle management for each instance.
- ✗
Use the 'for_each' meta-argument with a list of numbers.
Why it's wrong here
Using `for_each` with a list of numbers would iterate over each number in the list, but the module itself provisions only a single EC2 instance per iteration, so three numbers would yield three instances. This approach is tempting because `for_each` is commonly used to create multiple resources from a set of distinct keys, and it would work correctly here if the goal were to create three identical instances. However, the question asks for the *most efficient and concise* method; `for_each` requires explicitly defining a list (e.g., `[1, 2, 3]`), whereas the `count` meta-argument achieves the same result with a single integer, making it more concise for creating a fixed number of identical resources.
- ✗
Copy the module block three times with different names.
Why it's wrong here
Copying and pasting the entire module block three times, each with a unique name, directly violates the Don't Repeat Yourself (DRY) principle. While functionally it would create three instances, this approach is highly inefficient, error-prone, and significantly reduces maintainability. Any future changes to the module's configuration would require identical modifications across all three blocks, increasing the risk of inconsistencies and configuration drift.
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