Add ES_PRESET check to admin dashboard

app/lib/admin/system_check/elasticsearch_check.rb

@@ -15,7 +15,7 @@ def skip?
   def pass?
     return true unless Chewy.enabled?
 
-    running_version.present? && compatible_version? && cluster_health['status'] == 'green' && indexes_match?
+    running_version.present? && compatible_version? && cluster_health['status'] == 'green' && indexes_match? && preset_matches?
   rescue Faraday::ConnectionFailed, Elasticsearch::Transport::Transport::Error
     false
   end
@@ -39,8 +39,12 @@ def message
       )
     elsif cluster_health['status'] == 'red'
       Admin::SystemCheck::Message.new(:elasticsearch_health_red)
-    else
+    elsif cluster_health['number_of_nodes'] < 2 && ENV.fetch('ES_PRESET', 'single_node_cluster') != 'single_node_cluster'
+      Admin::SystemCheck::Message.new(:elasticsearch_preset_single_node, nil, 'https://docs.joinmastodon.org/admin/optional/elasticsearch/#scaling')
+    elsif cluster_health['status'] == 'yellow'
       Admin::SystemCheck::Message.new(:elasticsearch_health_yellow)
+    else
+      Admin::SystemCheck::Message.new(:elasticsearch_preset, nil, 'https://docs.joinmastodon.org/admin/optional/elasticsearch/#scaling')
     end
   rescue Faraday::ConnectionFailed, Elasticsearch::Transport::Transport::Error
     Admin::SystemCheck::Message.new(:elasticsearch_running_check)
@@ -86,4 +90,8 @@ def mismatched_indexes
   def indexes_match?
     mismatched_indexes.empty?
   end
+
+  def preset_matches?
+    (cluster_health['number_of_nodes'] < 2) == (ENV.fetch('ES_PRESET', 'single_node_cluster') == 'single_node_cluster')
+  end
 end

config/locales/en.yml

@@ -820,6 +820,12 @@ en:
         message_html: Elasticsearch cluster is unhealthy (yellow status), you may want to review your setup
       elasticsearch_index_mismatch:
         message_html: Elasticsearch index mappings are outdated. Please run <code>tootctl search deploy --only=%{value}</code>
+      elasticsearch_preset:
+        action: See documentation
+        message_html: Your Elastic Search cluster has more than one node, but is only using one.
+      elasticsearch_preset_single_node:
+        action: See documentation
+        message_html: Your Elastic Search cluster has only one node, <code>ES_PRESET</code> should be set to <code>single_node_cluster</code>.
       elasticsearch_running_check:
         message_html: Could not connect to Elasticsearch. Please check that it is running, or disable full-text search
       elasticsearch_version_check: