Flash a warning when not using index aliases

Changelog: changed
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71609
EE: true

ee/app/controllers/ee/admin/application_settings_controller.rb

@@ -9,6 +9,7 @@ module EE
       prepended do
         before_action :elasticsearch_reindexing_task, only: [:advanced_search]
         before_action :elasticsearch_index_settings, only: [:advanced_search]
+        before_action :elasticsearch_warn_if_not_using_aliases, only: [:advanced_search]
 
         feature_category :license, [:seat_link_payload]
         feature_category :source_code_management, [:templates]
@@ -22,6 +23,12 @@ module EE
         def elasticsearch_index_settings
           @elasticsearch_index_settings = Elastic::IndexSetting.order_by_name
         end
+
+        def elasticsearch_warn_if_not_using_aliases
+          @elasticsearch_warn_if_not_using_aliases = ::Gitlab::Elastic::Helper.default.alias_missing?
+        rescue StandardError => e
+          log_exception(e)
+        end
       end
 
       EE_VALID_SETTING_PANELS = %w(advanced_search templates).freeze

ee/app/views/admin/application_settings/advanced_search.html.haml

@@ -2,5 +2,22 @@
 - page_title _("Advanced Search")
 
 - @content_class = "limit-container-width" unless fluid_layout
+- help_link_start = "<a class='gl-link' href='#{help_page_path('integration/elasticsearch')}#%{anchor}' target='_blank' rel='noopener noreferrer'>"
+- help_zero_downtime_reindexing_link_start = help_link_start.html_safe % { anchor: "zero-downtime-reindexing" }
+- help_advanced_search_migrations_link_start = help_link_start.html_safe % { anchor: "advanced-search-migrations" }
+- help_recreate_index_link_start = help_link_start.html_safe % { anchor: "last-resort-to-recreate-an-index" }
+
+
+- if @elasticsearch_warn_if_not_using_aliases
+  - content_for :page_level_alert do
+    %div{ class: [container_class, @content_class, 'gl-pt-5!'] }
+      .gl-alert{ class: ['gl-alert-warning'] }
+        = sprite_icon('warning', size: 16, css_class: "gl-alert-icon")
+        .gl-alert-content{ role: 'alert' }
+          %h4.gl-alert-title
+            = s_('AdvancedSearch|Reindex required')
+          .gl-alert-body
+            = s_('Introduced in GitLab 13.1, before using %{reindexing_link_start}zero-downtime reindexing%{link_end} and %{migrations_link_start}Advanced Search migrations%{link_end}, you need to %{recreate_link_start}recreate your index%{link_end}.').html_safe % { reindexing_link_start: help_zero_downtime_reindexing_link_start, migrations_link_start: help_advanced_search_migrations_link_start, recreate_link_start: help_recreate_index_link_start, link_end: '</a>'.html_safe }
 
 = render_if_exists 'admin/application_settings/elasticsearch_form'
+

ee/lib/gitlab/elastic/helper.rb

@@ -164,6 +164,10 @@ module Gitlab
         client.indices.exists_alias(name: name || target_name)
       end
 
+      def alias_missing?(name: nil)
+        !alias_exists?(name: name)
+      end
+
       # Calls Elasticsearch refresh API to ensure data is searchable
       # immediately.
       # https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-refresh.html

ee/spec/controllers/admin/application_settings_controller_spec.rb

@@ -321,6 +321,33 @@ RSpec.describe Admin::ApplicationSettingsController do
       @request.env['HTTP_REFERER'] = advanced_search_admin_application_settings_path
     end
 
+    context 'warning if not using index aliases' do
+      let(:helper) { instance_double(::Gitlab::Elastic::Helper) }
+
+      before do
+        allow(::Gitlab::Elastic::Helper).to receive(:default).and_return(helper)
+      end
+
+      it 'warns when NOT using index aliases' do
+        allow(helper).to receive(:alias_missing?).and_return true
+        get :advanced_search
+        expect(assigns[:elasticsearch_warn_if_not_using_aliases]).to be_truthy
+      end
+
+      it 'does NOT warn when using index aliases' do
+        allow(helper).to receive(:alias_missing?).and_return false
+        get :advanced_search
+        expect(assigns[:elasticsearch_warn_if_not_using_aliases]).to be_falsy
+      end
+
+      it 'does NOT blow up if elasticsearch is unreachable' do
+        allow(helper).to receive(:alias_missing?).and_raise(::Elasticsearch::Transport::Transport::ServerError, 'boom')
+        get :advanced_search
+        expect(assigns[:elasticsearch_warn_if_not_using_aliases]).to be_falsy
+        expect(response).to have_gitlab_http_status(:ok)
+      end
+    end
+
     context 'advanced search settings' do
       it 'updates the advanced search settings' do
         settings = {

ee/spec/lib/ee/gitlab/elastic/helper_spec.rb

@@ -264,6 +264,12 @@ RSpec.describe Gitlab::Elastic::Helper, :request_store do
     end
   end
 
+  describe '#alias_missing?' do
+    it 'is the opposite of #alias_exists?' do
+      expect(helper.alias_missing?).to eq(!helper.alias_exists?)
+    end
+  end
+
   describe '#cluster_free_size_bytes' do
     it 'returns valid cluster size' do
       expect(helper.cluster_free_size_bytes).to be_positive

locale/gitlab.pot

@@ -2917,6 +2917,9 @@ msgstr ""
 msgid "Advanced export options"
 msgstr ""
 
+msgid "AdvancedSearch|Reindex required"
+msgstr ""
+
 msgid "After a successful password update you will be redirected to login screen."
 msgstr ""
 
@@ -18659,6 +18662,9 @@ msgstr ""
 msgid "Interval Pattern"
 msgstr ""
 
+msgid "Introduced in GitLab 13.1, before using %{reindexing_link_start}zero-downtime reindexing%{link_end} and %{migrations_link_start}Advanced Search migrations%{link_end}, you need to %{recreate_link_start}recreate your index%{link_end}."
+msgstr ""
+
 msgid "Introducing Your DevOps Reports"
 msgstr ""