Add rake task gitlab:elastic:list_pending_migrations

This will help people diagnose if there are pending migrations before
doing upgrades that might cause backwards compatibility issues.

doc/integration/elasticsearch.md

@@ -416,6 +416,7 @@ The following are some available Rake tasks:
 | [`sudo gitlab-rake gitlab:elastic:projects_not_indexed`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)             | Displays which projects are not indexed.                                                                                                                                                  |
 | [`sudo gitlab-rake gitlab:elastic:reindex_cluster`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)                  | Schedules a zero-downtime cluster reindexing task. This feature should be used with an index that was created after GitLab 13.0. |
 | [`sudo gitlab-rake gitlab:elastic:mark_reindex_failed`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)`]            | Mark the most recent re-index job as failed. |
+| [`sudo gitlab-rake gitlab:elastic:list_pending_migrations`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)`]        | List pending migrations. Pending migrations include those that have not yet started, have started but not finished and those that are halted. |
 
 ### Environment variables
 

ee/app/services/elastic/data_migration_service.rb

@@ -61,6 +61,12 @@ module Elastic
         end
       end
 
+      def pending_migrations
+        migrations.select do |migration|
+          !migration_has_finished?(migration.name_for_key)
+        end
+      end
+
       def halted_migrations?
         migrations.reverse.any? do |migration|
           migration_halted?(migration)

ee/changelogs/unreleased/rake-task-check-pending-migrations.yml

+---
+title: Add rake task to check pending Elasticsearch migrations
+merge_request: 54656
+author:
+type: added

ee/lib/tasks/gitlab/elastic.rake

@@ -149,6 +149,20 @@ namespace :gitlab do
       end
     end
 
+    desc "GitLab | Elasticsearch | List pending migrations"
+    task list_pending_migrations: :environment do
+      pending_migrations = ::Elastic::DataMigrationService.pending_migrations
+
+      if pending_migrations.any?
+        puts 'Pending migrations:'
+        pending_migrations.each do |migration|
+          puts migration.name
+        end
+      else
+        puts 'There are no pending migrations.'
+      end
+    end
+
     def project_id_batches(&blk)
       relation = Project.all
 

ee/spec/services/elastic/data_migration_service_spec.rb

@@ -188,4 +188,38 @@ RSpec.describe Elastic::DataMigrationService, :elastic do
       expect(subject.halted_migration).to eq(migration)
     end
   end
+
+  describe 'pending_migrations?' do
+    context 'when there is a pending migration' do
+      let(:migration) { subject.migrations.first }
+
+      before do
+        migration.save!(completed: false)
+      end
+
+      it 'returns true' do
+        expect(subject.pending_migrations?).to eq(true)
+      end
+    end
+
+    context 'when there is no pending migration' do
+      it 'returns false' do
+        expect(subject.pending_migrations?).to eq(false)
+      end
+    end
+  end
+
+  describe 'pending_migrations' do
+    let(:pending_migration1) { subject.migrations[1] }
+    let(:pending_migration2) { subject.migrations[2] }
+
+    before do
+      pending_migration1.save!(completed: false)
+      pending_migration2.save!(completed: false)
+    end
+
+    it 'returns only pending migrations' do
+      expect(subject.pending_migrations.map(&:name)).to eq([pending_migration1, pending_migration2].map(&:name))
+    end
+  end
 end

ee/spec/tasks/gitlab/elastic_rake_spec.rb

@@ -207,4 +207,28 @@ RSpec.describe 'gitlab:elastic namespace rake tasks', :elastic do
       end
     end
   end
+
+  describe 'list_pending_migrations' do
+    subject { run_rake_task('gitlab:elastic:list_pending_migrations') }
+
+    context 'when there are pending migrations' do
+      let(:pending_migration1) { ::Elastic::DataMigrationService.migrations[1] }
+      let(:pending_migration2) { ::Elastic::DataMigrationService.migrations[2] }
+
+      before do
+        pending_migration1.save!(completed: false)
+        pending_migration2.save!(completed: false)
+      end
+
+      it 'outputs pending migrations' do
+        expect { subject }.to output(/#{pending_migration1.name}\n#{pending_migration2.name}/).to_stdout
+      end
+    end
+
+    context 'when there is no pending migrations' do
+      it 'outputs message there are no pending migrations' do
+        expect { subject }.to output(/There are no pending migrations./).to_stdout
+      end
+    end
+  end
 end