How would you reference the module output vpc_id?

To reference the output of a module in Terraform, the syntax follows a specific structure. The correct answer demonstrates this structure perfectly.

When you declare a module in Terraform, you typically do so within the configuration, and any outputs from that module can be accessed using the prefix module.<MODULE_NAME>.<OUTPUT_NAME>. In this scenario, assuming that the module is named "vpc" and it has an output variable named "vpc_id", the expression module.vpc.vpc_id accurately reflects that hierarchy.

This structure clearly indicates that you are looking for the output value vpc_id from the module called vpc. The use of the module prefix is essential, as it tells Terraform that you are accessing a resource generated by a module rather than a resource or data source at the root level of your configuration.

Other answer choices do not conform to the correct syntax for accessing module outputs, making them invalid options. For example, option A suggests an incorrect structure without the proper prefix. Options C and D also misrepresent how to reference outputs and lack the necessary module context. Understanding this syntax is critical to effectively using Terraform modules and accessing their outputs.