Advanced Search: Estimate ES cluster size

This change introduces a new rake task estimate_cluster_size,
which could be useful for estimating ES cluster size

doc/integration/elasticsearch.md

@@ -56,6 +56,12 @@ A few notes on CPU and storage:
   to any spinning media for Elasticsearch. In testing, nodes that use SSD storage
   see boosts in both query and indexing performance.
 
+- We've introduced the [`estimate_cluster_size`](#gitlab-advanced-search-rake-tasks)
+  Rake task to estimate the Advanced Search storage requirements in advance, which
+- The [`estimate_cluster_size`](#gitlab-advanced-search-rake-tasks) Rake task estimates the
+  Advanced Search storage requirements in advance. The Rake task uses total repository size
+  for the calculation. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/221177) in GitLab 13.10.
+
 Keep in mind, these are **minimum requirements** for Elasticsearch.
 Heavily-used Elasticsearch clusters will likely require considerably more
 resources.
@@ -421,8 +427,9 @@ The following are some available Rake tasks:
 | [`sudo gitlab-rake gitlab:elastic:index_snippets`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)                   | Performs an Elasticsearch import that indexes the snippets data.                                                                                                                          |
 | [`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. |
+| [`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. |
+| [`sudo gitlab-rake gitlab:elastic:estimate_cluster_size`](https://gitlab.com/gitlab-org/gitlab/blob/master/ee/lib/tasks/gitlab/elastic.rake)            | Get an estimate of cluster size based on the total repository size. |
 
 ### Environment variables
 

ee/changelogs/unreleased/221177-estimate-es-cluster-size.yml

+---
+title: 'Advanced Search: Estimate Elasticsearch cluster size'
+merge_request: 54430
+author:
+type: added

ee/lib/tasks/gitlab/elastic.rake

@@ -163,6 +163,21 @@ namespace :gitlab do
       end
     end
 
+    desc "GitLab | Elasticsearch | Estimate Cluster size"
+    task estimate_cluster_size: :environment do
+      include ActionView::Helpers::NumberHelper
+
+      total_size = Namespace::RootStorageStatistics.sum(:repository_size).to_i
+      total_size_human = number_to_human_size(total_size, delimiter: ',', precision: 1, significant: false)
+
+      estimated_cluster_size = total_size * 0.5
+      estimated_cluster_size_human = number_to_human_size(estimated_cluster_size, delimiter: ',', precision: 1, significant: false)
+
+      puts "This GitLab instance repository size is #{total_size_human}."
+      puts "By our estimates for such repository size, your cluster size should be at least #{estimated_cluster_size_human}.".color(:green)
+      puts 'Please note that it is possible to index only selected namespaces/projects by using Elasticsearch indexing restrictions.'
+    end
+
     def project_id_batches(&blk)
       relation = Project.all
 

ee/spec/tasks/gitlab/elastic_rake_spec.rb

@@ -231,4 +231,18 @@ RSpec.describe 'gitlab:elastic namespace rake tasks', :elastic do
       end
     end
   end
+
+  describe 'estimate_cluster_size' do
+    subject { run_rake_task('gitlab:elastic:estimate_cluster_size') }
+
+    before do
+      create(:namespace_root_storage_statistics, repository_size: 1.megabyte)
+      create(:namespace_root_storage_statistics, repository_size: 10.megabyte)
+      create(:namespace_root_storage_statistics, repository_size: 30.megabyte)
+    end
+
+    it 'outputs estimates' do
+      expect { subject }.to output(/your cluster size should be at least 20.5 MB/).to_stdout
+    end
+  end
 end