How to use Terraform in a cloud agnostic way

Question

I have seen many examples on how to use Terraform to launch AWS resources. I have also seen many claims that Terraform is cloud agnostic.

What I have not seen is an

Answer 1

@ydaetskcoR I love your idea of the provider specific modules (which follow an interface). But the change I would propose is that they can be called from the main.tf file directly with a variable there to determine the module source.

So I would keep:
modules/google/dns/record/main.tf
modules/aws/dns/record/main.tf

I would not use modules/generic/dns/record/main.tf

And add:
main.tf

variable "cloud_provider" = { default = "aws" }  
module "dns" {  
  source = "modules/${var.cloud_provider}/dns/record/main.tf"  
  domain_name_record = "${var.domain_name_record}"  
  domain_name_zone   = "${var.domain_name_zone}"  
  domain_name_target = "${var.domain_name_target}"  
}

Unfortunately Terraform doesn't support variable module source.
See: https://github.com/hashicorp/terraform/issues/1439

I'm considering ways to add a plugin or perhaps even a higher level template abstraction.