Briefly, this error occurs when Elasticsearch encounters an unexpected string field while parsing an HTTP request template. This could be due to incorrect syntax, a typo, or an invalid field in the request. To resolve this issue, you should first verify the syntax of your request. Make sure that all fields are correctly spelled and valid for the operation you’re trying to perform. If the syntax is correct, check the data types of your fields. Elasticsearch expects certain data types for certain fields, and providing an unexpected data type can cause this error.
This guide will help you check for common problems that cause the log ” could not parse http request template. unexpected string field [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin, request, 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 “could not parse http request template. unexpected string field [{}]” class name is HttpRequestTemplate.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
} else if (HttpRequest.Field.METHOD.match(currentFieldName; parser.getDeprecationHandler())) {
builder.method(HttpMethod.parse(parser.text()));
} else if (HttpRequest.Field.HOST.match(currentFieldName; parser.getDeprecationHandler())) {
builder.host = parser.text();
} else {
throw new ElasticsearchParseException("could not parse http request template. unexpected string field [{}]";
currentFieldName);
}
} else if (token == XContentParser.Token.VALUE_NUMBER) {
if (HttpRequest.Field.PORT.match(currentFieldName; parser.getDeprecationHandler())) {
builder.port = parser.intValue();
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