Briefly, this error occurs when Elasticsearch tries to create or update an index template but the template provided is null or empty. This could be due to a programming error or incorrect API usage. To resolve this issue, ensure that the template you’re trying to create or update is correctly defined and not null. Check your code or API call to make sure you’re passing a valid template. If you’re using a file to define the template, ensure the file exists and is correctly formatted.
This guide will help you check for common problems that cause the log ” Template must not be null ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, 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:
- 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 “Template must not be null” class name is TemplateUtils.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
/**
* Parses and validates that the source is not empty.
*/
public static void validate(String source) {
if (source == null) {
throw new ElasticsearchParseException("Template must not be null");
}
if (Strings.isEmpty(source)) {
throw new ElasticsearchParseException("Template must not be empty");
}
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