A dynamic template must be defined with a name – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when you’re trying to create a dynamic template in Elasticsearch without providing a name. Dynamic templates in Elasticsearch require a unique name for identification. To resolve this issue, you should ensure that you provide a unique name when defining your dynamic template. Also, check your syntax to ensure it’s correct. If you’re using an API, ensure that the request body includes the template name.

This guide will help you check for common problems that cause the log ” A dynamic template must be defined with a name ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: index, template.

 
 

index

Overview

In Elasticsearch, an index (plural: indices) contains a schema and can have one or more shards and replicas. An Elasticsearch index is divided into shards and each shard is an instance of a Lucene index.

Indices are used to store the documents in dedicated data structures corresponding to the data type of fields. For example, text fields are stored inside an inverted index whereas numeric and geo fields are stored inside BKD trees.

Examples

Create index

The following example is based on Elasticsearch version 5.x onwards. An index with two shards, each having one replica will be created with the name test_index1

PUT /test_index1?pretty
{
    "settings" : {
        "number_of_shards" : 2,
        "number_of_replicas" : 1
    },
    "mappings" : {
        "properties" : {
            "tags" : { "type" : "keyword" },
            "updated_at" : { "type" : "date" }
        }
    }
}

List indices

All the index names and their basic information can be retrieved using the following command:

GET _cat/indices?v

Index a document

Let’s add a document in the index with the command below:

PUT test_index1/_doc/1
{
  "tags": [
    "opster",
    "elasticsearch"
  ],
  "date": "01-01-2020"
}

Query an index

GET test_index1/_search
{
  "query": {
    "match_all": {}
  }
}

Query multiple indices

It is possible to search multiple indices with a single request. If it is a raw HTTP request, index names should be sent in comma-separated format, as shown in the example below, and in the case of a query via a programming language client such as python or Java, index names are to be sent in a list format.

GET test_index1,test_index2/_search

Delete indices

DELETE test_index1

Common problems

  • It is good practice to define the settings and mapping of an Index wherever possible because if this is not done, Elasticsearch tries to automatically guess the data type of fields at the time of indexing. This automatic process may have disadvantages, such as mapping conflicts, duplicate data and incorrect data types being set in the index. If the fields are not known in advance, it’s better to use dynamic index templates.
  • Elasticsearch supports wildcard patterns in Index names, which sometimes aids with querying multiple indices, but can also be very destructive too. For example, It is possible to delete all the indices in a single command using the following commands:
DELETE /*

To disable this, you can add the following lines in the elasticsearch.yml:

action.destructive_requires_name: true
 
 

template

If you want to learn more about Elasticsearch templates, check out this guide.

Overview

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.
  2. 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.
 
 

Log Context

Log “A dynamic template must be defined with a name” class name is RootObjectMapper.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 List tmplNodes = (List) fieldNode;
 List templates = new ArrayList<>();
 for (Object tmplNode : tmplNodes) {
 Map tmpl = (Map) tmplNode;
 if (tmpl.size() != 1) {
 throw new MapperParsingException("A dynamic template must be defined with a name");
 }
 Map.Entry entry = tmpl.entrySet().iterator().next();
 String templateName = entry.getKey();
 Map templateParams = (Map) entry.getValue();
 DynamicTemplate template = DynamicTemplate.parse(templateName; templateParams);

 

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