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

Opster Team

July-20, Version: 1.7-8.0

Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many configuration errors.

Briefly, this error occurs when a template in Elasticsearch contains an unknown key. This can be due to a typo in the template or an outdated template. To resolve this issue, you can check the syntax of the template and ensure that all keys are correct.

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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, indices and template.

 
 

admin

 
 

indices

 
 

template

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 “unknown key [{}] in the template”classname  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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