use cluster data for default replication (#106)

CHANGELOG.md

@@ -49,6 +49,7 @@
 - [Improvement] Introduce cookie based sessions management for future usage.
 - [Improvement] Introduce config validation.
 - [Improvement] Provide flash messages support.
+- [Improvement] Use replication factor of two by default (if not overridden) for Web UI topics when there is more than one broker.
 - [Fix] Return 402 status instead of 500 on Pro features that are not available in OSS.
 - [Fix] Fix a case where errors would not be visible without Rails due to the `String#first` usage.
 - [Fix] Fix a case where live-poll would be disabled but would still update data.

lib/karafka/web/cli.rb

@@ -12,20 +12,24 @@ class Cli < Thor
       method_option(
         :replication_factor,
         desc: 'Replication factor for created topics',
-        default: 1,
+        default: false,
+        check_default_type: false,
         type: :numeric
       )
       # Installs Karafka Web. Creates all needed topics, populates the data and adds the needed
       # code to `karafka.rb`.
       def install
-        Karafka::Web::Installer.new.install(replication_factor: options[:replication_factor])
+        Karafka::Web::Installer.new.install(
+          replication_factor: compute_replication_factor(options[:replication_factor])
+        )
       end
 
       desc 'migrate', 'Creates necessary topics if not present and populates state data'
       method_option(
         :replication_factor,
         desc: 'Replication factor for created topics',
-        default: 1,
+        default: false,
+        check_default_type: false,
         type: :numeric
       )
       # Creates new topics (if any) and populates missing data.
@@ -37,27 +41,44 @@ def install
       #   2. When upgrading Web-UI in-between versions that would require extra topics and/or extra
       #      states populated.
       def migrate
-        Karafka::Web::Installer.new.migrate(replication_factor: options[:replication_factor])
+        Karafka::Web::Installer.new.migrate(
+          replication_factor: compute_replication_factor(options[:replication_factor])
+        )
       end
 
       desc 'reset', 'Resets the Web UI by removing all the Web topics and creating them again'
       method_option(
         :replication_factor,
         desc: 'Replication factor for created topics',
-        default: 1,
+        default: false,
+        check_default_type: false,
         type: :numeric
       )
       # Resets Karafka Web. Removes the topics, creates them again and populates the initial state
       # again. This is useful in case the Web-UI metrics or anything else got corrupted.
       def reset
-        Karafka::Web::Installer.new.reset(replication_factor: options[:replication_factor])
+        Karafka::Web::Installer.new.reset(
+          replication_factor: compute_replication_factor(options[:replication_factor])
+        )
       end
 
       desc 'uninstall', 'Removes all the Web UI topics and the enabled code'
       # Uninstalls Karafka Web
       def uninstall
         Karafka::Web::Installer.new.uninstall
       end
+
+      private
+
+      # Takes the CLI user provided replication factor but if not present, uses the brokers count
+      # to decide. For non-dev clusters (with one broker) we usually want to have replication of
+      # two, just to have some redundancy.
+      # @param cli_replication_factor [Integer, false] user requested replication factor or false
+      #   if we are supposed to compute the factor automatically
+      # @return [Integer] replication factor for Karafka Web UI topics
+      def compute_replication_factor(cli_replication_factor)
+        cli_replication_factor || Ui::Models::ClusterInfo.fetch.brokers.size > 1 ? 2 : 1
+      end
     end
   end
 end