Briefly, this error occurs when you try to create an index template in Elasticsearch without providing any content in the template. Elasticsearch requires a valid JSON object to define the settings and mappings for the index template. To resolve this issue, ensure that you are providing a valid JSON object in the body of the request when creating the index template. This JSON object should include the necessary settings and mappings for the index template. If you are using a file to provide the template, make sure the file is not empty and contains valid JSON.
This guide will help you check for common problems that cause the log ” Template must not be empty ” 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 empty” class name is TemplateUtils.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
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");
} try {
XContentHelper.convertToMap(JsonXContent.jsonXContent; source; false);
} catch (Exception e) {
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