What is the value of the local $vhost_file variable when defined as $vhost_file = template("${module_name}/vhost.erb")?

The value of the local $vhost_file variable is determined by the expression used to define it. In this case, when you assign $vhost_file with the result of the template() function, you are invoking Puppet's built-in function that processes the specified template file—${module_name}/vhost.erb. The template() function compiles the template located in the respective module's directory, replacing any variables defined within that template with their corresponding values.

Thus, the correct understanding is that the value of the variable is the result produced by the template function once the template file is processed. This means that $vhost_file will hold the rendered content of the vhost.erb template, making it a representation of the output generated by the template function. It is that rendering process and the functionality of the template function that defines the value being assigned to the variable.