Use Gitlab Terraform state

.gitlab-ci.yml

 image: busybox:latest
 
+cache:
+  key: manifests-elastic
+  paths:
+    - ${TF_ROOT}/.terraform
+
+# docs: https://docs.gitlab.com/ee/user/infrastructure/iac/terraform_state.html#get-started-using-gitlab-ci
 elastic:
   stage: deploy
   tags:
@@ -8,10 +14,13 @@ elastic:
     image: registry.gitlab.com/gitlab-org/terraform-images/stable:latest
     entrypoint: [""]
   variables:
+    TF_ROOT: ${CI_PROJECT_DIR}/manifests/elastic
+    TF_ADDRESS: ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/terraform/state/manifests/elastic
     TF_VAR_ec_apikey: $EC_API_KEY
   script:
-    - cd ./manifests/elastic
+    - cd ${TF_ROOT}
     - terraform init 
+    - terraform validate
     - terraform fmt -check
     - terraform plan
     - terraform apply -auto-approve