terraform get: can't use variable in module source parameter?

[amaczuga]

I'm trying to avoid hard-coding module sources; the simplest approach would be:

variable "foo_module_source" {
  default = "github.com/thisisme/terraform-foo-module"
}

module "foo" {
  source = "${var.foo_module_source}"
}

The result I get while attempting to run terraform get -update is

Error loading Terraform: Error downloading modules: error downloading module 'file:///home/thisisme/terraform-env/${var.foo_module_source}': source path error: stat /home/thisisme/terraform-env/${var.foo_module_source}: no such file or directory

[radeksimko]

I'm trying to avoid hard-coding module sources

Is there any particular reason behind that? Do you expect some modules to have the same interface, so you can swap these?

[mitchellh]

This is as intended. We should add validation that this isn't allowed.

The reason is simply that it breaks our compile -> semantic check -> execute loop. i.e. imagine if your C code could arbitrarily download new C files during compile/execution. Would be weird.

[amaczuga]

Do you expect some modules to have the same interface

yes, that is exactly my point - for the flexible running plans against various versions/forks of identically interfaced modules, without refactoring base terraform code

[amaczuga]

This is as intended.

Er. Forgive me - I'm lost here, due to labels - that is - marked bug, yet your comment suggest a wontfix

[radeksimko]

marked bug, yet your comment suggest a wontfix

The fix is to add the validation so you get something a bit more clear rather than "error downloading module" I guess.

[clstokes]

FWIW, this is something I wanted to do as well and found wasn't supported. In my case, I wanted to avoid duplicating git::ssh://git@github.com/... across tens or hundreds of files and do something like source = "${var.module_path}//modules/common-vpc".

[clstokes]

Also to set the branch/tag via a variable would be helpful...

[radeksimko]

Also to set the branch/tag via a variable would be helpful...

See #1145

[clstokes]

@radeksimko I'm familiar with ref as added in a recent version, but I'm suggesting something like source = "github.com/clstokes/terraform-modules//modules/common-vpc?ref=${var.module_branch}".

Are variables allowed at all in modules sources?

[mitchellh]

@clstokes They're not yet