When defining variables in Terraform, which of the following options allows for a default value?

When defining variables in Terraform, specifying a default value is accomplished by using the default argument within the variable block. This allows the variable to have a preset value that Terraform will use if no other value is provided during runtime.

By including the default argument, you enable greater flexibility in your Terraform configurations. Users can still override the default value by providing their own input when running Terraform commands, allowing for both predefined and customizable configurations. This ease of use can significantly streamline the deployment process, as it reduces the need for every variable to be explicitly set while still maintaining the capability for customization.

In contrast, a variable defined with no default means that it is required to be provided during execution, otherwise Terraform will produce an error stating that the input variable is not set. A mandatory variable is simply another way of saying that the variable does not have a default and must be supplied, and an optional variable without a default also cannot have a preset value. Thus, only the variable defined with a default argument can allow a default value to be utilized.