Terraformの出力を別のTerraformで利用する ref: http://qiita.com/atsaki/items/d4678c1d62093fef47ec

file0.txt

$ mkdir -p ~/terraform-remote/repo1
$ cd ~/terraform-remote/repo1
$ cat << EOS > repo1.tf
output "repo1_output" {
  value = "Output from repo1"
}
EOS

file1.txt

$ terraform remote config -backend consul -backend-config="path=repo1"
Initialized blank state with remote state enabled!
Remote state configured and pulled.

file2.txt

$ terraform apply

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

  repo1_output = Output from repo1

file3.txt

$ mkdir -p ~/terraform-remote/repo2
$ cd ~/terraform-remote/repo2
$ cat << EOS > repo2.tf
resource "terraform_remote_state" "repo1" {                                 
    backend = "consul"                                                              
    config {                                                                       
        path = "repo1"    
    }                                                                              
} 

output "repo1_output" {
  value = "\${terraform_remote_state.repo1.output.repo1_output}"
}
EOS

file4.txt

$ terraform apply
terraform_remote_state.repo1: Creating...
  backend:     "" => "consul"
  config.#:    "" => "1"
  config.path: "" => "repo1"
  output.#:    "" => "<computed>"
terraform_remote_state.repo1: Creation complete

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

The state of your infrastructure has been saved to the path
below. This state is required to modify and destroy your
infrastructure, so keep it safe. To inspect the complete state
use the `terraform show` command.

State path: terraform.tfstate

Outputs:

  repo1_output = Output from repo1

file5.txt

$ cd ~/terraform-remote/repo1
$ cat << EOS > repo1.tf
output "repo1_output" {
  value = "Modified output from repo1"
}
EOS
$ terraform apply

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

  repo1_output = Modified output from repo1

file6.txt

$ cd ~/terraform-remote/repo2
$ terraform apply
terraform_remote_state.repo1: Refreshing state... (ID: 2015-04-04 10:34:03.745421914 +0000 UTC)

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

  repo1_output = Modified output from repo1