Terraform Module Configuration: Input Variables, Outputs, and Best Practices

• ✓ A.A module should define variables for any values that need to be customized by the calling configuration.
• B.A module should assume the calling configuration will provide all necessary provider configurations.
• C.A module must have all Terraform code in a single main.tf file.
• ✓ D.A module can be sourced from the same repository as the root module using a relative path.
• E.A module should rely on direct attribute references to resources in the calling configuration.

Why A: Terraform modules are designed to be reusable and configurable. **Statement A**: By defining input variables for any customizable values (e.g., resource names, sizes, regions), the module abstracts away hardcoded details and allows the calling configuration to pass in specific values via variable assignments. This follows the principle of encapsulation, where the module's internal logic remains unchanged while its behavior adapts to the caller's needs. **Statement D**: Modules can be sourced from various locations, including local paths relative to the calling configuration. This is a common pattern for organizing smaller, internal modules within the same repository or project directory, allowing for modularity without requiring separate version control repositories for every small module.

• A.The count meta-argument is not supported on module blocks.
• B.Module outputs are automatically available as inputs to other modules in the same configuration.
• C.Module sources must include a version constraint to ensure reproducibility.
• ✓ D.A module can be called multiple times in the same configuration with different input variables.
• ✓ E.The source attribute of a module can be a Git repository URL with a specific commit SHA.

Why D: Terraform modules can be called multiple times with different input variables, enabling reuse. Option E is correct because module sources can be Git repository URLs with a specific commit SHA (e.g., using `?ref=<sha>`). Option A is incorrect because the `count` meta-argument is supported on module blocks in Terraform 0.13 and later. Option B is incorrect because module outputs are not automatically available; they must be referenced explicitly as `module.<module_name>.<output_name>`. Option C is incorrect because version constraints are optional for reproducibility; they are recommended but not mandatory.

• A.Use the same provider configuration as the root module.
• ✓ B.Use local values to simplify expressions.
• C.Hardcode default values for all variables.
• D.Define outputs for all resources created.
• E.Use absolute paths in module source.

Why B: Options B and D are correct. Using local values (B) simplifies expressions and improves readability within a module, as recommended by Terraform best practices. Defining outputs (D) for resources that need to be consumed by the root module or other modules enables proper data flow and reusability. Option A is incorrect because relying on the same provider configuration as the root module reduces module portability; explicit provider configurations are preferred. Option C is incorrect because hardcoding default values reduces flexibility for module consumers; variables should have sensible defaults but allow overrides. Option E is incorrect because absolute paths make modules less portable; relative paths or module registries are preferred.

• ✓ A.The module requires a variable 'environment' that is not passed.
• B.The module block syntax is incorrect.
• C.The variable 'vpc_cidr' is misspelled.
• D.The variable 'vpc_cidr' conflicts with a provider variable.

Why A: The error 'Missing required variable' indicates that a variable required by the module has not been provided. Even though 'vpc_cidr' is supplied, the module likely defines a required input variable named 'environment' without a default value, and the user did not pass it in the module block. Terraform enforces that all required variables without defaults must be explicitly set by the caller.

• A.Set required_providers inside the module to include the alias.
• ✓ B.Use the providers argument in the module block: providers = { aws = aws.uswest }.
• C.Include a provider block inside the module block with alias = 'uswest'.
• D.Do nothing; Terraform automatically uses the default provider.

Why B: Terraform uses the `providers` argument in a module block to explicitly map provider configurations from the root module into the module. Since the root module has two AWS provider configurations (default and `uswest` alias), and the module requires the us-west alias, the mapping `providers = { aws = aws.uswest }` ensures the module uses the aliased provider. Without this explicit mapping, Terraform would default to the root module's default provider, which may not have the correct region or settings.