Add migration self monitoring environment

changelogs/unreleased/204858-update-self-monitor-environments.yml

+---
+title: Add migration to create self monitoring project environment
+merge_request: 25289
+author:
+type: added

db/post_migrate/20200214214934_create_environment_for_self_monitoring_project.rb

+# frozen_string_literal: true
+
+class CreateEnvironmentForSelfMonitoringProject < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def up
+    execute <<~SQL
+      INSERT INTO environments (project_id, name, slug, created_at, updated_at)
+      SELECT instance_administration_project_id, 'production', 'production', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP
+      FROM application_settings
+      WHERE instance_administration_project_id IS NOT NULL
+      AND NOT EXISTS (
+        SELECT 1
+        FROM environments
+        INNER JOIN application_settings
+        ON application_settings.instance_administration_project_id = environments.project_id
+      )
+    SQL
+  end
+
+  def down
+    # no-op
+
+    # This migration cannot be reversed because it cannot be ensured that the environment for the Self Monitoring Project
+    # did not already exist before the migration ran - in that case, the migration does nothing, and it would be unexpected
+    # behavior for that environment to be deleted by reversing this migration.
+  end
+end

spec/migrations/create_environment_for_self_monitoring_project_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200214214934_create_environment_for_self_monitoring_project')
+
+describe CreateEnvironmentForSelfMonitoringProject, :migration do
+  let(:application_settings_table) { table(:application_settings) }
+
+  let(:environments) { table(:environments) }
+
+  let(:instance_administrators_group) do
+    table(:namespaces).create!(
+      id: 1,
+      name: 'GitLab Instance Administrators',
+      path: 'gitlab-instance-administrators-random',
+      type: 'Group'
+    )
+  end
+
+  let(:self_monitoring_project) do
+    table(:projects).create!(
+      id: 2,
+      name: 'Self Monitoring',
+      path: 'self_monitoring',
+      namespace_id: instance_administrators_group.id
+    )
+  end
+
+  context 'when the self monitoring project ID is not set' do
+    it 'does not make changes' do
+      expect(environments.find_by(project_id: self_monitoring_project.id)).to be_nil
+
+      migrate!
+
+      expect(environments.find_by(project_id: self_monitoring_project.id)).to be_nil
+    end
+  end
+
+  context 'when the self monitoring project ID is set' do
+    before do
+      application_settings_table.create!(instance_administration_project_id: self_monitoring_project.id)
+    end
+
+    context 'when the environment already exists' do
+      let!(:environment) do
+        environments.create!(project_id: self_monitoring_project.id, name: 'production', slug: 'production')
+      end
+
+      it 'does not make changes' do
+        expect(environments.find_by(project_id: self_monitoring_project.id)).to eq(environment)
+
+        migrate!
+
+        expect(environments.find_by(project_id: self_monitoring_project.id)).to eq(environment)
+      end
+    end
+
+    context 'when the environment does not exist' do
+      it 'creates the environment' do
+        expect(environments.find_by(project_id: self_monitoring_project.id)).to be_nil
+
+        migrate!
+
+        expect(environments.find_by(project_id: self_monitoring_project.id)).to be
+      end
+    end
+  end
+end