terraform state move between multiple files demo

terraform-state-demo.files

==> ./module <==
==> ./module/main.tf <==
variable "msg" {}
resource "null_resource" "goodbye" {
  provisioner "local-exec" {
      command =  "echo ${var.msg}"
  }
}

==> ./main.tf <==
resource "null_resource" "hello" {
  provisioner "local-exec" {
    command =  "echo hello world"
  }
}

module "goodbye-mundo" {
  source = "./module"
  msg = "goodbye mundo"
}

==> ./run.sh <==
#! /usr/bin/env bash 
rm -f *tfstate*

OLD_STATE_FILE=terraform.tfstate
NEW_STATE_FILE=new.tfstate

OLD_RESOURCE_ADDRESS=module.goodbye-mundo.null_resource.goodbye
NEW_RESOURCE_ADDRESS=null_resource.goodbye

function tf_apply {
  terraform apply -auto-approve
}

function tf_mv_state {
  terraform state mv \
    -state=${OLD_STATE_FILE} \
    -state-out=${NEW_STATE_FILE} \
    ${OLD_RESOURCE_ADDRESS} ${NEW_RESOURCE_ADDRESS}
}

function tf_reset_new_state {
  terraform state rm \
    -state=${NEW_STATE_FILE} \
    null_resource.goodbye
}

echo "Ready to start?"
select yn in "Yes" "No"; do
  case $yn in
    Yes ) tf_apply; break;;
    No ) exit;;
  esac
done

echo
echo "Terraform should have cleanly applied creating a state file: ${OLD_STATE_FILE}"
echo "This file should contain two resources:"
echo " - A top-level resource: null_resource.hello"
echo " - A module w/ a single resource: ${OLD_RESOURCE_ADDRESS}"
echo

echo "Move inner module (${OLD_RESOURCE_ADDRESS}) state?"
select yn in "Yes" "No"; do
  case $yn in
    Yes ) tf_mv_state; break;;
    No ) exit;;
  esac
done

echo
echo "Terraform should have moved the inner-module (${OLD_RESOURCE_ADDRESS}) to ${NEW_STATE_FILE} at the address ${NEW_RESOURCE_ADDRESS}"
echo

echo "Reset new state file ${NEW_STATE_FILE}?"
select yn in "Yes" "No"; do
  case $yn in
    Yes ) tf_reset_new_state; break;;
    No ) exit;;
  esac
done