Fix Elastic::MigrationWorker current_migration (2nd attempt)

ee/app/models/elastic/migration_record.rb

@@ -65,8 +65,6 @@ module Elastic
             .search(index: helper.migrations_index_name, body: { query: { term: { completed: completed } }, size: ELASTICSEARCH_SIZE })
             .dig('hits', 'hits')
             .map { |v| v['_id'].to_i }
-    rescue StandardError
-      []
     end
 
     def running?

ee/app/workers/elastic/migration_worker.rb

@@ -21,6 +21,13 @@ module Elastic
       return false unless helper.alias_exists?
 
       in_lock(self.class.name.underscore, ttl: 1.day, retries: 10, sleep_sec: 1) do
+        # migration index should be checked before pulling the current_migration because if no migrations_index exists,
+        # current_migration will return nil
+        unless helper.migrations_index_exists?
+          logger.info 'MigrationWorker: creating migrations index'
+          helper.create_migrations_index
+        end
+
         migration = current_migration
 
         unless migration
@@ -28,11 +35,6 @@ module Elastic
           break false
         end
 
-        unless helper.migrations_index_exists?
-          logger.info 'MigrationWorker: creating migrations index'
-          helper.create_migrations_index
-        end
-
         if migration.halted?
           logger.info "MigrationWorker: migration[#{migration.name}] has been halted. All future migrations will be halted because of that. Exiting"
           unpause_indexing!(migration)
@@ -89,7 +91,12 @@ module Elastic
     def current_migration
       completed_migrations = Elastic::MigrationRecord.load_versions(completed: true)
 
+      # use a negative condition to support new migrations which do not exist in the index yet
       Elastic::DataMigrationService.migrations.find { |migration| !completed_migrations.include?(migration.version) }
+    rescue StandardError => e
+      # do not return a migration if there is an issue communicating with the Elasticsearch instance
+      logger.error("MigrationWorker: #{e.class}: #{e.message}")
+      nil
     end
 
     def pause_indexing!(migration)

ee/spec/models/elastic/migration_record_spec.rb

@@ -42,13 +42,13 @@ RSpec.describe Elastic::MigrationRecord, :elastic do
   end
 
   describe '#load_from_index' do
-    it 'does not raise an exeption when connection refused' do
+    it 'does not raise an exception when connection refused' do
       allow(Gitlab::Elastic::Helper.default).to receive(:get).and_raise(Faraday::ConnectionFailed)
 
       expect(record.load_from_index).to be_nil
     end
 
-    it 'does not raise an exeption when record does not exist' do
+    it 'does not raise an exception when record does not exist' do
       allow(Gitlab::Elastic::Helper.default).to receive(:get).and_raise(Elasticsearch::Transport::Transport::Errors::NotFound)
 
       expect(record.load_from_index).to be_nil
@@ -95,18 +95,18 @@ RSpec.describe Elastic::MigrationRecord, :elastic do
       expect(described_class.load_versions(completed: false)).to contain_exactly(in_progress_migration.version)
     end
 
-    it 'returns empty array if no index present' do
+    it 'raises an exception if no index present' do
       es_helper.delete_migrations_index
 
-      expect(described_class.load_versions(completed: true)).to eq([])
-      expect(described_class.load_versions(completed: false)).to eq([])
+      expect { described_class.load_versions(completed: true) }.to raise_exception(Elasticsearch::Transport::Transport::Errors::NotFound)
+      expect { described_class.load_versions(completed: false) }.to raise_exception(Elasticsearch::Transport::Transport::Errors::NotFound)
     end
 
-    it 'returns empty array when exception is raised' do
+    it 'raises an exception when exception is raised' do
       allow(Gitlab::Elastic::Helper.default.client).to receive(:search).and_raise(Faraday::ConnectionFailed)
 
-      expect(described_class.load_versions(completed: true)).to eq([])
-      expect(described_class.load_versions(completed: false)).to eq([])
+      expect { described_class.load_versions(completed: true) }.to raise_exception(StandardError)
+      expect { described_class.load_versions(completed: false) }.to raise_exception(StandardError)
     end
   end
 

ee/spec/tasks/gitlab/elastic_rake_spec.rb

@@ -69,7 +69,6 @@ RSpec.describe 'gitlab:elastic namespace rake tasks', :elastic, :silence_stdout
 
     it 'marks all migrations as completed' do
       expect(Elastic::DataMigrationService).to receive(:mark_all_as_completed!).and_call_original
-      expect(Elastic::MigrationRecord.load_versions(completed: true)).to eq([])
 
       subject
       refresh_index!