Fix #2: Unique state and runner for a given pipeline

This commit makes state filename unique for a given pipeline (and
remove this state in the cleaning phase), and adds a unique tag to the
runners created for the pipeline for jobs not to be run in runners
from other pipelines that run in parallel.

.gitlab-ci.yml

 variables:
   CI_TEMPLATE_REGISTRY_HOST: registry.gitlab.inria.fr
-  TF_STATE_NAME: default
+  TF_STATE_NAME: pipeline-$CI_PIPELINE_ID
+  TF_VAR_CI_PIPELINE_ID: $CI_PIPELINE_ID
+
+workflow:
+  rules:
+    - if: $CLOUDSTACK_API_KEY
 
 include:
   - template: Terraform/Base.gitlab-ci.yml  # https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/ci/templates/Terraform/Base.gitlab-ci.yml
@@ -32,20 +37,23 @@ deploy:
     - small
   script:
     - cp $SSH_PRIVATE_KEY id_rsa
-    - gitlab-terraform plan -var runner_count=0
-    - gitlab-terraform apply
-    - gitlab-terraform plan -var runner_count=3
+    - gitlab-terraform plan
     - gitlab-terraform apply
 
+# Variable interpolation on job tags do not expand $CI_PIPELINE_ID
+
 execute:
   stage: execute
   image: alpine
   parallel:
     matrix:
       - index: [0, 1, 2]
+  variables:
+    PIPELINE_ID: $CI_PIPELINE_ID
   tags:
     - terraform
     - docker
+    - pipeline-$PIPELINE_ID
     - runner-$index
   script:
     - echo Greetings from runner $index!
@@ -58,6 +66,6 @@ cleanup:
   script:
     - cd "${TF_ROOT}"
     - cp $SSH_PRIVATE_KEY id_rsa
-    - gitlab-terraform plan -var runner_count=0
-    - gitlab-terraform apply
+    - gitlab-terraform destroy
+    - 'curl --user "gitlab-ci-token:$CI_JOB_TOKEN" --request DELETE "$CI_API_V4_URL/projects/$CI_PROJECT_ID/terraform/state/$TF_STATE_NAME"'
   when: always

cloud-init.sh.tftpl

@@ -16,7 +16,7 @@
   # We install docker.io to be able to register a docker executor
   apt-get install --yes gitlab-runner docker.io
   gitlab-runner register --non-interactive \
-    --tag-list terraform,docker,runner-${index} \
+    --tag-list terraform,docker,pipeline-${CI_PIPELINE_ID},runner-${index} \
     --executor docker --docker-image alpine --url https://gitlab.inria.fr \
     --registration-token ${REGISTRATION_TOKEN}
 ) >>/root/log.txt 2>&1

main.tf

@@ -24,13 +24,13 @@ variable "SSH_PUBLIC_KEY" {
   type = string
 }
 
-variable "runner_count" {
+variable "CI_PIPELINE_ID" {
   type = number
 }
 
 resource "cloudstack_instance" "runner" {
-  count            = var.runner_count
-  name             = "gitlabcigallery-terraform-runner-${count.index}"
+  count            = 3
+  name             = "gitlabcigallery-terraform-pipeline-${var.CI_PIPELINE_ID}-${count.index}"
   service_offering = "Custom"
   template         = "ubuntu-20.04-lts"
   zone             = "zone-ci"
@@ -43,6 +43,7 @@ resource "cloudstack_instance" "runner" {
     index              = count.index
     REGISTRATION_TOKEN = var.REGISTRATION_TOKEN
     SSH_PUBLIC_KEY     = var.SSH_PUBLIC_KEY
+    CI_PIPELINE_ID     = var.CI_PIPELINE_ID
   })
   connection {
     type                = "ssh"