How should you correctly pass the value of variable num_servers into a module with the input servers?

In Terraform, when passing values to modules, it is essential to reference variables correctly. The syntax var.variable_name is specifically used to access input variables declared in a Terraform configuration. By using var.num_servers, you indicate that you are referring to the variable named num_servers defined in the module's context.

This clear and direct reference ensures that Terraform understands you are pulling the value of num_servers as it has been defined in the parent's scope, allowing for proper passing into the module's servers input. Terraform processes this correctly in the context of its variable resolution engine, ensuring that the input value is recognized and handled as intended during infrastructure planning and deployment.

Other options do not adhere to the correct syntax for passing variables to modules within Terraform. For example, using servers = num_servers does not specify that num_servers is a variable and could lead to errors since Terraform would look for a resource or another construct by that name instead. The other syntax options, like ${num_servers} or ${var.num_servers}, reference older interpolation syntax that has been largely superseded by the more straightforward referencing format using var.variable_name.