Briefly, this error occurs when Elasticsearch encounters an empty template ID during its operations. This could be due to a configuration error or a bug in the system. To resolve this issue, you can check your Elasticsearch configuration to ensure that all template IDs are correctly defined. If the problem persists, consider updating your Elasticsearch version or contacting support for further assistance. Additionally, ensure that your data input does not contain empty template IDs.
This guide will help you check for common problems that cause the log ” empty template [” + id + “] found and dropped ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: 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 “empty template [” + id + “] found and dropped” classname is ScriptMetadata.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
// as of 8.0 we drop scripts/templates with an empty source
// this check should be removed for the next upgradable version after 8.0
// since there is a guarantee no more empty scripts will exist
if (source.getSource().isEmpty()) {
if (Script.DEFAULT_TEMPLATE_LANG.equals(source.getLang())) {
logger.warn("empty template [" + id + "] found and dropped");
} else {
logger.warn("empty script [" + id + "] found and dropped");
}
} else {
scripts.put(id; source);
