Manage template fails if settings section is missing

[tmanninger]

• Version: 7.6.1
• Operating System: Debian 10

If the logstash output plugin "elasticsearch" manage the lifecycle management, adding lifecycle settings to the template fails, if template have no "settings" section declared.

logstash output plugin:

output {
      elasticsearch {
          hosts =>  [ 'https://localhost:9200' ]
          ilm_enabled => true
          ilm_rollover_alias => "syslog"
          ilm_pattern => "{now/d}-000001"
          ilm_policy => "long"
          manage_template => true
          template => "/etc/logstash/template.d/syslog.json"
          template_name => "syslog"
          template_overwrite => true
          ....
      }
}

If the template file /etc/logstash/template.d/syslog.json have no "settings {}" section declared, logstash fails with the following error:

Failed to install template. {:message=>"undefined method `update' for nil:NilClass", :class=>"NoMethodError", :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-elasticsearch-10.3.1-java/lib/logstash/outputs/elasticsearch/template_manager.rb:39:in `add_ilm_settings_to_template'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-elasticsearch-10.3.1-java/lib/logstash/outputs/elasticsearch/template_manager.rb:14:in `install_template'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-elasticsearch-10.3.1-java/lib/logstash/outputs/elasticsearch/common.rb:197:in `install_template'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-output-elasticsearch-10.3.1-java/lib/logstash/outputs/elasticsearch/common.rb:53:in `block in setup_after_successful_connection'"]}

If i add an empty settings section to the template, then it works:

{
  "settings" : { },
   ....
}

See vendor/bundle/jruby/2.5.0/gems/logstash-output-elasticsearch-10.3.1-java/lib/logstash/outputs/elasticsearch/template_manager.rb on line 39:

      # Overwrite any index patterns, and use the rollover alias. Use 'index_patterns' rather than 'template' for pattern
      # definition - remove any existing definition of 'template'
      template.delete('template') if template.include?('template')
      template['index_patterns'] = "#{plugin.ilm_rollover_alias}-*"
      if template['settings'] && (template['settings']['index.lifecycle.name'] || template['settings']['index.lifecycle.rollover_alias'])
        plugin.logger.info("Overwriting index lifecycle name and rollover alias as ILM is enabled.")
      end
      template['settings'].update({ 'index.lifecycle.name' => plugin.ilm_policy, 'index.lifecycle.rollover_alias' => plugin.ilm_rollover_alias})
    end

Logstash assumes, that the "settings" part exists. Before add the lifecycle settings, it must be checked, if the settings part exists...

[hackery]

This probably needs re-raising in project logstash-plugins/logstash-output-elasticsearch.
The file referenced by the above comment is template_manager.rb