Unknown key in the template – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch encounters an unrecognized key in the index template. This could be due to a typo, incorrect syntax, or usage of a key that is not supported in the current version of Elasticsearch. To resolve this issue, you should first verify the keys used in your template against the Elasticsearch documentation for your version. Ensure that the keys are correctly spelled and properly formatted. If the error persists, consider updating your Elasticsearch version or modifying your template to exclude the problematic key.

This guide will help you check for common problems that cause the log ” unknown key [{}] in the template ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: admin, template, indices.

 
 

admin

 
 

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.
 
 

indices

Log Context

Log “unknown key [{}] in the template” class name is PutIndexTemplateRequest.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 mapping((Map) entry1.getValue());
 }
 } else if (name.equals("aliases")) {
 aliases((Map) entry.getValue());
 } else {
 throw new ElasticsearchParseException("unknown key [{}] in the template "; name);
 }
 }
 return this;
 }

 

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