Background migration to force migration to Hashed Storage

The background migration is using existing migration code from
hashed storage migration rake task.

changelogs/unreleased/246655-hashed-storage-trigger-migration-to-hashed-storage-via-post-deploy.yml

+---
+title: 'Hashed Storage: forced automatic migration of legacy projects via background jobs'
+merge_request: 42313
+author:
+type: changed

db/post_migrate/20200915044225_schedule_migration_to_hashed_storage.rb

+# frozen_string_literal: true
+
+class ScheduleMigrationToHashedStorage < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+  DOWNTIME = false
+  MIGRATION = 'MigrateToHashedStorage'
+
+  disable_ddl_transaction!
+
+  def up
+    migrate_async(MIGRATION)
+  end
+
+  def down
+    # NO-OP
+  end
+end

db/schema_migrations/20200915044225

+0c659c7cbbda4d2fbbbd344f0fca50860ccf54ec8b666772d53a4c6fa602d097
\ No newline at end of file

lib/gitlab/background_migration/migrate_to_hashed_storage.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Background migration to move any legacy project to Hashed Storage
+    class MigrateToHashedStorage
+      def perform
+        batch_size = helper.batch_size
+        legacy_projects_count = Project.with_unmigrated_storage.count
+
+        if storage_migrator.rollback_pending?
+          logger.warn(
+            migrator: 'MigrateToHashedStorage',
+            message: 'Aborting an storage rollback operation currently in progress'
+          )
+
+          storage_migrator.abort_rollback!
+        end
+
+        if legacy_projects_count == 0
+          logger.info(
+            migrator: 'MigrateToHashedStorage',
+            message: 'There are no projects requiring migration to Hashed Storage'
+          )
+
+          return
+        end
+
+        logger.info(
+          migrator: 'MigrateToHashedStorage',
+          message: "Enqueuing migration of #{legacy_projects_count} projects in batches of #{batch_size}"
+        )
+
+        helper.project_id_batches_migration do |start, finish|
+          storage_migrator.bulk_schedule_migration(start: start, finish: finish)
+
+          logger.info(
+            migrator: 'MigrateToHashedStorage',
+            message: "Enqueuing migration of projects in batches of #{batch_size} from ID=#{start} to ID=#{finish}",
+            batch_from: start,
+            batch_to: finish
+          )
+        end
+      end
+
+      private
+
+      def helper
+        Gitlab::HashedStorage::RakeHelper
+      end
+
+      def storage_migrator
+        @storage_migrator ||= Gitlab::HashedStorage::Migrator.new
+      end
+
+      def logger
+        @logger ||= ::Gitlab::BackgroundMigration::Logger.build
+      end
+    end
+  end
+end

spec/lib/gitlab/background_migration/migrate_to_hashed_storage_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+# rubocop:disable RSpec/FactoriesInMigrationSpecs
+RSpec.describe Gitlab::BackgroundMigration::MigrateToHashedStorage, :sidekiq, :redis do
+  let(:migrator) { Gitlab::HashedStorage::Migrator.new }
+
+  subject(:background_migration) { described_class.new }
+
+  describe '#perform' do
+    let!(:project) { create(:project, :empty_repo, :legacy_storage) }
+
+    context 'with pending rollback' do
+      it 'aborts rollback operation' do
+        Sidekiq::Testing.disable! do
+          Sidekiq::Client.push(
+            'queue' => ::HashedStorage::ProjectRollbackWorker.queue,
+            'class' => ::HashedStorage::ProjectRollbackWorker,
+            'args' => [project.id]
+          )
+
+          expect { background_migration.perform }.to change { migrator.rollback_pending? }.from(true).to(false)
+        end
+      end
+    end
+
+    it 'enqueues legacy projects to be migrated' do
+      Sidekiq::Testing.fake! do
+        expect { background_migration.perform }.to change { Sidekiq::Queues[::HashedStorage::MigratorWorker.queue].size }.by(1)
+      end
+    end
+
+    context 'when executing all jobs' do
+      it 'migrates legacy projects' do
+        Sidekiq::Testing.inline! do
+          expect { background_migration.perform }.to change { project.reload.legacy_storage? }.from(true).to(false)
+        end
+      end
+    end
+  end
+end
+# rubocop:enable RSpec/FactoriesInMigrationSpecs

spec/migrations/20200915044225_schedule_migration_to_hashed_storage_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200915044225_schedule_migration_to_hashed_storage.rb')
+
+RSpec.describe ScheduleMigrationToHashedStorage, :sidekiq do
+  describe '#up' do
+    it 'schedules background migration job' do
+      Sidekiq::Testing.fake! do
+        expect { migrate! }.to change { BackgroundMigrationWorker.jobs.size }.by(1)
+      end
+    end
+  end
+end