How To Solve Issues Related to Log – Realm is in user-dn-template mode:

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Updated: Jan-20

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Troubleshooting background

To troubleshoot Elasticsearch log “Realm is in user-dn-template mode:” it’s important to understand common problems related to Elasticsearch concepts: plugin. See detailed explanations below complete with common problems, examples and useful tips.

Plugin in Elasticsearch

What it is

A plugin is used to enhance the core functionalities of Elasticsearch. Elasticsearch provides some core plugins as a part of their release installation. In addition to those core plugins, it is possible to write your own custom plugins as well. There are several community plugins available on GitHub for various use cases.

Examples:
  • Get all the instructions for the plugin usage
sudo bin/elasticsearch-plugin -h
  • Installing S3 plugin using URL for storing Elasticsearch snapshots on S3
sudo bin/elasticsearch-plugin install repository-s3
  • Removing a plugin
sudo bin/elasticsearch-plugin remove repository-s3
  • Installing a plugin using the file path
sudo bin/elasticsearch-plugin install file:///path/to/plugin.zip

Notes:
  • Plugins are installed and removed using the elasticsearch-plugin script, which ships as a part of Elasticsearch installation and can be found inside the bin/ directory of the Elasticsearch installation path.
  • A plugin has to be installed on every node of the cluster and each of the nodes has to be restarted to make the plugin visible.
  • You can also download the plugin manually and then install it using the elasticsearch-plugin install command, providing the file name/path of the plugin’s source file.
  • When a plugin is removed, you will need to restart every elasticsearch node in order to complete the removal process.

Common Problems:
  • Managing permission issues during and after plugin installation is the most common problem. If Elasticsearch was installed using the deb or rpm package then the plugin has to be installed using the root user, or else you can install the plugin as the user that owns all of the Elasticsearch files.
  • In case of deb or rpm package installation, it is important to check the permission of the plugins directory after plugin installation and update the permission if it has been modified using the following command:
chown -R elasticsearch:elasticsearch path_to_plugin_directory 
  • If your Elasticsearch nodes are running in a private subnet without internet access, you cannot install a plugin directly. In this case, you can simply download the plugins at once and copy the files inside the plugins directory of the Elasticsearch installation path on every node. The node has to be restarted in this case as well.

Template in Elasticsearch

What it is

A template in Elasticsearch falls into  one of the two following categories and is  indexed inside Elasticsearch using its dedicated endpoint: 

  1. Index Templates, which are a way to define a set of rules including index settings, mappings and an index pattern. The template is applied automatically whenever a new index is created with the matching pattern. Templates are also used to dynamically apply custom mapping for the fields which are not predefined inside existing mapping.
  1. Search Templates, which help in defining templates for search queries using mustache scripting language. These templates act as a placeholder for variables defined inside the search queries.
Examples

Create a dynamic index template

PUT /_template/template_1?pretty
{
  "index_patterns": [
    "logs*",
    "api*"
  ],
  "settings": {
    "number_of_shards": 2
  },
  "mappings": {
    "dynamic_templates": [
      {
        "strings": {
          "match_mapping_type": "string",
          "mapping": {
            "type": "keyword"
          }
        }
      }
    ],
    "properties": {
      "host_name": {
        "type": "keyword"
      },
      "created_at": {
        "type": "date"
      }
    }
  }
}

Create a search template

POST /_scripts/search_template_1?pretty
{
    "script": {
        "lang": "mustache",
        "source": {
            "query": {
                "match": {
                    "description": "{{query_string}}"
                }
            }
        }
    }
}

Executing a search query using search template

GET /_search/template?pretty
{
    "id": "search_template_1", 
    "params": {
        "query_string": "hello world"
    }
}

The search request will be executed by default on all the indices available in the cluster and can be limited to particular indices using an index parameter.

Notes

A dynamic index template is always useful when you do not know the field names in advance and want to control their mapping as per the business use case.


To help troubleshoot related issues we have gathered selected Q&A from the community and issues from Github , please review the following for further information :

1 Uld Not Resolve Placeholder In Stri  

2Ring Circular Placeholder Reference  


Log Context

Log ”Realm [{}] is in user-dn-template mode: [{}]” classname is LdapSessionFactory.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

         userDnTemplates = LdapSessionFactorySettings.USER_DN_TEMPLATES_SETTING.get(settings).toArray(Strings.EMPTY_ARRAY);
        if (userDnTemplates.length == 0) {
            throw new IllegalArgumentException("missing required LDAP setting ["
                    + RealmSettings.getFullSettingKey(config; LdapSessionFactorySettings.USER_DN_TEMPLATES_SETTING) + "]");
        }
        logger.info("Realm [{}] is in user-dn-template mode: [{}]"; config.name(); userDnTemplates);
        groupResolver = groupResolver(settings);
        metaDataResolver = new LdapMetaDataResolver(settings; ignoreReferralErrors);
    }

    /**






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