How best to handle multiple .tfvars files that use common .tf files?

Question

I am going to be managing the CDN configurations of dozens of applications through Terraform. I have a set of .tf files holding all the default constant settings that are common among all configurations and then each application has its own .tfvars file to hold its unique settings.

If I run something like terraform apply --var-file=app1.tfvars --var-file=app2.tfvars --var-file=app3.tfvars then only the last file passed in is used.

Even if this did work it will become unmanageable when I extend this to more sites.

What is the correct way to incorporate multiple .tfvars files that populate a common set of .tf files?

Edit: I should add that the .tfvar files define the same variables but with different values. I need to declare state of the resources defined in the .tf files once for each .tfvar file.

Answer 1

I found the best way to handle this case (without any 3rd party tools is to use) Terraform workspaces and create a separate workspace for each .tfvars file. This way I can use the same common .tf files and simply swap to a different workspace with terraform workspace select <workspace name> before running terraform apply --var-file=<filename> with each individual .tfvars file.