Build cloud native images on tags

When on a tag, trigger a multi-project pipeline in the CNG repostiory.

Opting for a trigger rather than an addition to our release-tools
project for a few reasons:

- The Dockerfiles in the CNG image repo change infrequently, and as a result
I don't feel the need/overhead for stable branches in that repo at this time
- My intent with the CNG repo, is that once stable, the Dockerfiles
would actualy move to their component projects, to be versioned with the
code they are building
- It is likely that we will want to followup with a manually triggered package
for branches for devs, and possibly review apps, so it made sense to
build the CNG ci jobs to accept this sort of pipeline.

.gitlab-ci.yml

@@ -298,6 +298,25 @@ review-docs-cleanup:
   script:
     - ./trigger-build-docs cleanup
 
+##
+# Trigger a docker image build in CNG (Cloud Native GitLab) repository
+#
+cloud-native-image:
+  image: ruby:2.4-alpine
+  before_script: []
+  stage: build
+  allow_failure: true
+  cache: {}
+  retry: 0
+  before_script:
+    - gem install gitlab --no-doc
+    - chmod 755 ./scripts/trigger-build-cloud-native
+  script:
+    - ./scripts/trigger-build-cloud-native
+  only:
+    - tags@gitlab-org/gitlab-ce
+    - tags@gitlab-org/gitlab-ee
+
 # Retrieve knapsack and rspec_flaky reports
 retrieve-tests-metadata:
   <<: *tests-metadata-state

scripts/trigger-build-cloud-native

@@ -0,0 +1,61 @@
+#!/usr/bin/env ruby
+
+require 'gitlab'
+
+#
+# Configure credentials to be used with gitlab gem
+#
+Gitlab.configure do |config|
+  config.endpoint = 'https://gitlab.com/api/v4'
+end
+
+#
+# The remote project
+#
+GITLAB_CNG_REPO = 'gitlab-org/build/CNG'.freeze
+
+def ee?
+  ENV['CI_PROJECT_NAME'] == 'gitlab-ee' || File.exist?('CHANGELOG-EE.md')
+end
+
+def read_file_version(filename)
+  raw_version = File.read(filename).strip
+
+  # if the version matches semver format, treat it as a tag and prepend `v`
+  if raw_version =~ Regexp.compile(/^\d+\.\d+\.\d+(-rc\d+)?(-ee)?$/)
+    "v#{raw_version}"
+  else
+    raw_version
+  end
+end
+
+def params
+  params = {
+    'GITLAB_SHELL_VERSION' => read_file_version('GITLAB_SHELL_VERSION'),
+    'GITALY_VERSION' => read_file_version('GITALY_SERVER_VERSION'),
+    'TRIGGERED_USER' => ENV['GITLAB_USER_NAME'],
+    'TRIGGER_SOURCE' => "https://gitlab.com/gitlab-org/#{ENV['CI_PROJECT_NAME']}/-/jobs/#{ENV['CI_JOB_ID']}"
+  }
+
+  if ee?
+    params['EE_PIPELINE'] = 'true'
+    params['GITLAB_EE_VERSION'] = ENV['CI_COMMIT_REF_NAME']
+  else
+    params['CE_PIPELINE'] = 'true'
+    params['GITLAB_CE_VERSION'] = ENV['CI_COMMIT_REF_NAME']
+  end
+
+  params
+end
+
+#
+# Trigger a pipeline
+#
+def trigger_pipeline
+  # Create the cross project pipeline using CI_JOB_TOKEN
+  pipeline = Gitlab.run_trigger(GITLAB_CNG_REPO, ENV['CI_JOB_TOKEN'], 'master', params)
+
+  puts "Triggered https://gitlab.com/#{GITLAB_CNG_REPO}/pipelines/#{pipeline.id}"
+end
+
+trigger_pipeline