Add `release-environments` child pipeline setup and build images

Part of https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/2674

In order to have commits to stable branches able to be deployed to
release environments for deployment testing and validation, we need
to build imags with the CNG project containing the contents of the
stable branches.

This change adds the work to get images built through the `CNG-mirror`
project for use by the release environments. These will only be built
on commits to a stable branch.

.gitlab-ci.yml

@@ -12,6 +12,7 @@ stages:
   - post-qa
   - pages
   - notify
+  - release-environments
 
 # always use `gitlab-org` runners, however
 # in cases where jobs require Docker-in-Docker, the job

.gitlab/ci/release-environments.gitlab-ci.yml

+---
+start-release-environments-pipeline:
+  allow_failure: true
+  extends:
+    - .release-environments:rules:start-release-environments-pipeline
+  stage: release-environments
+  # We do not want to have ALL global variables passed as trigger variables,
+  # as they cannot be overridden. See this issue for more context:
+  #
+  # https://gitlab.com/gitlab-org/gitlab/-/issues/387183
+  inherit:
+    variables: false
+
+  # These variables are set in the pipeline schedules.
+  # They need to be explicitly passed on to the child pipeline.
+  # https://docs.gitlab.com/ee/ci/pipelines/multi_project_pipelines.html#pass-cicd-variables-to-a-downstream-pipeline-by-using-the-variables-keyword
+  variables:
+    # This is needed by `release-environments-build-cng-env` (`.gitlab/ci/release-environments/main.gitlab-ci.yml`).
+    PARENT_PIPELINE_ID: $CI_PIPELINE_ID
+  trigger:
+    strategy: depend
+    include: .gitlab/ci/release-environments/main.gitlab-ci.yml

.gitlab/ci/release-environments/main.gitlab-ci.yml

+---
+default:
+  interruptible: true
+
+stages:
+  - prepare
+
+include:
+  - local: .gitlab/ci/global.gitlab-ci.yml
+
+release-environments-build-cng-env:
+  allow_failure: true
+  image: ${GITLAB_DEPENDENCY_PROXY_ADDRESS}ruby:${RUBY_VERSION}-alpine3.16
+  stage: prepare
+  needs:
+    # We need this job because we need its `cached-assets-hash.txt` artifact, so that we can pass the assets image tag to the downstream CNG pipeline.
+    - pipeline: $PARENT_PIPELINE_ID
+      job: build-assets-image
+  variables:
+    BUILD_ENV: build.env
+  before_script:
+    - source ./scripts/utils.sh
+    - install_gitlab_gem
+  script:
+    - 'ruby -r./scripts/trigger-build.rb -e "puts Trigger.variables_for_env_file(Trigger::CNG.new.variables)" > $BUILD_ENV'
+    - echo "GITLAB_ASSETS_TAG=$(assets_image_tag)" >> $BUILD_ENV
+    - ruby -e 'puts "FULL_RUBY_VERSION=#{RUBY_VERSION}"' >> build.env
+    - cat $BUILD_ENV
+  artifacts:
+    reports:
+      dotenv: $BUILD_ENV
+    paths:
+      - $BUILD_ENV
+    expire_in: 7 days
+    when: always
+
+release-environments-build-cng:
+  allow_failure: true
+  stage: prepare
+  needs: ["release-environments-build-cng-env"]
+  inherit:
+    variables: false
+  variables:
+    GITLAB_REF_SLUG: "${GITLAB_REF_SLUG}"
+    # CNG pipeline specific variables
+    GITLAB_VERSION: "${GITLAB_VERSION}"
+    GITLAB_TAG: "${GITLAB_TAG}"
+    GITLAB_ASSETS_TAG: "${GITLAB_ASSETS_TAG}"
+    FORCE_RAILS_IMAGE_BUILDS: "${FORCE_RAILS_IMAGE_BUILDS}"
+    CE_PIPELINE: "${CE_PIPELINE}"  # Based on https://docs.gitlab.com/ee/ci/jobs/job_control.html#check-if-a-variable-exists, `if: '$CE_PIPELINE'` will evaluate to `false` when this variable is empty
+    EE_PIPELINE: "${EE_PIPELINE}"  # Based on https://docs.gitlab.com/ee/ci/jobs/job_control.html#check-if-a-variable-exists, `if: '$EE_PIPELINE'` will evaluate to `false` when this variable is empty
+    GITLAB_ELASTICSEARCH_INDEXER_VERSION: "${GITLAB_ELASTICSEARCH_INDEXER_VERSION}"
+    GITLAB_KAS_VERSION: "${GITLAB_KAS_VERSION}"
+    GITLAB_METRICS_EXPORTER_VERSION: "${GITLAB_METRICS_EXPORTER_VERSION}"
+    GITLAB_PAGES_VERSION: "${GITLAB_PAGES_VERSION}"
+    GITLAB_SHELL_VERSION: "${GITLAB_SHELL_VERSION}"
+    GITALY_SERVER_VERSION: "${GITALY_SERVER_VERSION}"
+    RUBY_VERSION: "${FULL_RUBY_VERSION}"
+  trigger:
+    project: gitlab-org/build/CNG-mirror
+    branch: $TRIGGER_BRANCH
+    strategy: depend

.gitlab/ci/rules.gitlab-ci.yml

@@ -1905,6 +1905,13 @@
       when: never
     - if: '$CI_SERVER_HOST == "gitlab.com" && $CI_PROJECT_PATH == "gitlab-org/gitlab" && $CI_COMMIT_REF_NAME =~ /^[\d-]+-stable-ee$/'
 
+.releases:rules:canonical-dot-com-gitlab-stable-branch-only-setup-test-env-patterns:
+  rules:
+    - if: '$CI_COMMIT_MESSAGE =~ /\[merge-train skip\]/'
+      when: never
+    - if: '$CI_SERVER_HOST == "gitlab.com" && $CI_PROJECT_PATH == "gitlab-org/gitlab" && $CI_COMMIT_REF_NAME =~ /^[\d-]+-stable-ee$/'
+      changes: *setup-test-env-patterns
+
 .releases:rules:canonical-dot-com-security-gitlab-stable-branch-only:
   rules:
     - if: '$CI_COMMIT_MESSAGE =~ /\[merge-train skip\]/'
@@ -2299,3 +2306,14 @@
     - <<: *if-dot-com-gitlab-org-merge-request
       changes: *feature-flag-development-config-patterns
       allow_failure: true  # See https://gitlab.com/gitlab-org/gitlab/-/issues/351136
+
+##############################
+# release-environments rules #
+##############################
+.release-environments:rules:start-release-environments-pipeline:
+  rules:
+    - <<: *if-not-ee
+      when: never
+    - <<: *if-merge-request-labels-pipeline-expedite
+      when: never
+    - !reference [".releases:rules:canonical-dot-com-gitlab-stable-branch-only-setup-test-env-patterns", rules]