Read, generate and modify configuration →hardMultiple ChoiceObjective-mapped

TF-004 Read, generate and modify configuration Practice Question

A team wants to reuse a VPC module across multiple environments. They need to pass outputs from one module as inputs to another. Which configuration is correct?

⚠ Common exam trap

Many candidates confuse Terraform's module output syntax with the `outputs` block used in root modules or with AWS CloudFormation's `Fn::GetAtt`, leading them to add an extra `.outputs` or omit the `module.` prefix.

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

✓

module "vpc" { source = "./vpc" } module "app" { source = "./app" subnet_id = module.vpc.subnet_id }

In Terraform, module outputs are accessed using the syntax `module.<module_name>.<output_name>`, not `module.<module_name>.outputs.<output_name>` or `vpc.output.<output_name>`. The `outputs` attribute is not a valid path; Terraform automatically exposes all declared outputs of a module as attributes of the module object. Therefore, `module.vpc.subnet_id` correctly references the `subnet_id` output from the `vpc` module.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
module "vpc" { source = "./vpc" } module "app" { source = "./app" subnet_id = module.vpc.outputs.subnet_id }
Why it's wrong here
The syntax `module.vpc.outputs.subnet_id` is incorrect because Terraform directly exposes module outputs as attributes of the module instance itself. The `outputs` keyword is not part of the standard reference path for accessing module outputs. Instead, outputs from a module are accessed using the format `module.<MODULE_NAME>.<OUTPUT_NAME>`, making `module.vpc.subnet_id` the correct and idiomatic reference.
✗
module "vpc" { source = "./vpc" } module "app" { source = "./app" subnet_id = vpc.output.subnet_id }
Why it's wrong here
This option presents two distinct syntax errors: `vpc.output.subnet_id` incorrectly omits the `module.` prefix required to reference a named module instance, and it uses `.output` instead of directly referencing the output name. Terraform requires the full `module.<MODULE_NAME>.<OUTPUT_NAME>` syntax to correctly resolve the value exported by the module. Without `module.`, Terraform cannot identify the source of the `vpc` reference as a module instance.
✓
module "vpc" { source = "./vpc" } module "app" { source = "./app" subnet_id = module.vpc.subnet_id }
Why this is correct
This option correctly demonstrates the standard and recommended way to reference an output value from a Terraform module. The syntax `module.vpc.subnet_id` directly accesses the `subnet_id` output defined within the `vpc` module. This allows the `app` module to receive the necessary resource ID, establishing an explicit dependency and enabling resource sharing between different module instances.
✗
module "app" { source = "./app" subnet_id = module.vpc.subnet_id }
Why it's wrong here
This configuration is incorrect because it attempts to reference `module.vpc.subnet_id` without first defining a module named `vpc` in the current configuration. Terraform requires that any module instance referenced, such as `module.vpc`, must be explicitly declared using a `module` block with a unique name. Without the `module "vpc" { ... }` definition, Terraform cannot resolve the reference, leading to a configuration error during validation or planning.

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TF-004 Read, generate and modify configuration Practice Question

Why each option matters

Option-by-option breakdown

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