Briefly, this error occurs when Elasticsearch is unable to parse the index template due to incorrect syntax, invalid JSON format, or unsupported fields. To resolve this issue, you can validate your JSON format using a JSON validator. Ensure that the syntax is correct and all necessary fields are included. Also, check if the template is compatible with your Elasticsearch version. If the error persists, consider simplifying your template or breaking it down into smaller parts to isolate the problematic section.
This guide will help you check for common problems that cause the log ” Cannot parse the template [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: template, plugin.
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:
- 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.
- 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 “Cannot parse the template [{}]” classname is TemplateUtils.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
MapmappingMap = (Map ) typeMappingMap.get(key); if (containsCorrectVersion(versionKey; mappingMap; predicate) == false) { return false; } } catch (ElasticsearchParseException e) { logger.error(new ParameterizedMessage("Cannot parse the template [{}]"; templateName); e); throw new IllegalStateException("Cannot parse the template " + templateName; e); } } return true; }
