Briefly, this error occurs when the Elasticsearch HTTP client cannot verify the SSL/TLS certificate of the server it’s trying to connect to. This could be due to an expired certificate, a self-signed certificate, or a certificate from an untrusted source. To resolve this issue, you can either update the certificate with a valid one from a trusted Certificate Authority, or configure the Elasticsearch client to trust the server’s certificate. If it’s a self-signed certificate, you need to add it to the client’s truststore. Always ensure your certificates are up-to-date to avoid such issues.
This guide will help you check for common problems that cause the log ” Http client did not trust this server’s certificate; closing connection {} ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: client and plugin.
Overview
Any application that interfaces with Elasticsearch to index, update or search data, or to monitor and maintain Elasticsearch using various APIs can be considered a client
It is very important to configure clients properly in order to ensure optimum use of Elasticsearch resources.
Examples
There are many open-source client applications for monitoring, alerting and visualization, such as ElasticHQ, Elastalerts, and Grafana to name a few. On top of Elastic client applications such as filebeat, metricbeat, logstash and kibana that have all been designed to integrate with Elasticsearch.
However it is frequently necessary to create your own client application to interface with Elasticsearch. Below is a simple example of the python client (taken from the client documentation):
from datetime import datetime
from elasticsearch import Elasticsearch
es = Elasticsearch()
doc = {
'author': 'Testing',
'text': 'Elasticsearch: cool. bonsai cool.',
'timestamp': datetime.now(),
}
res = es.index(index="test-index", doc_type='tweet', id=1, body=doc)
print(res['result'])
res = es.get(index="test-index", doc_type='tweet', id=1)
print(res['_source'])
es.indices.refresh(index="test-index")
res = es.search(index="test-index", body={"query": {"match_all": {}}})
print("Got %d Hits:" % res['hits']['total']['value'])
for hit in res['hits']['hits']:
print("%(timestamp)s %(author)s: %(text)s" % hit["_source"])
All of the official Elasticsearch clients follow a similar structure, working as light wrappers around the Elasticsearch rest API, so if you are familiar with Elasticsearch query structure they are usually quite straightforward to implement.
Notes and Good Things to Know
Use official Elasticsearch libraries.
Although it is possible to connect with Elasticsearch using any HTTP method, such as a curl request, the official Elasticsearch libraries have been designed to properly implement connection pooling and keep-alives.
Official Elasticsearch clients are available for java, javascript, Perl, PHP, python, ruby and .NET. Many other programming languages are supported by community versions.
Keep your Elasticsearch version and client versions in sync.
To avoid surprises, always keep your client versions in line with the Elasticsearch version you are using. Always test clients with Elasticsearch since even minor version upgrades can cause issues due to dependencies or a need for code changes.
Load balance across appropriate nodes.
Make sure that the client properly load balances across all of the appropriate nodes in the cluster. In small clusters this will normally mean only across data nodes (never master nodes), or in larger clusters, all dedicated coordinating nodes (if implemented) .
Ensure that the Elasticsearch application properly handles exceptions.
In the case of Elasticsearch being unable to cope with the volume of requests, designing a client application to handle this gracefully (such as through some sort of queueing mechanism) will be better than simply inundating a struggling cluster with repeated requests.
Overview
A plugin is used to enhance the core functionalities of Elasticsearch. Elasticsearch provides some core plugins as a part of their release installation. In addition to those core plugins, it is possible to write your own custom plugins as well. There are several community plugins available on GitHub for various use cases.
Examples
Get all of the instructions for the plugin:
sudo bin/elasticsearch-plugin -h
Installing the S3 plugin for storing Elasticsearch snapshots on S3:
sudo bin/elasticsearch-plugin install repository-s3
Removing a plugin:
sudo bin/elasticsearch-plugin remove repository-s3
Installing a plugin using the file’s path:
sudo bin/elasticsearch-plugin install file:///path/to/plugin.zip
Notes and good things to know
- Plugins are installed and removed using the elasticsearch-plugin script, which ships as a part of the Elasticsearch installation and can be found inside the bin/ directory of the Elasticsearch installation path.
- A plugin has to be installed on every node of the cluster and each of the nodes has to be restarted to make the plugin visible.
- You can also download the plugin manually and then install it using the elasticsearch-plugin install command, providing the file name/path of the plugin’s source file.
- When a plugin is removed, you will need to restart every Elasticsearch node in order to complete the removal process.
Common issues
- Managing permission issues during and after plugin installation is the most common problem. If Elasticsearch was installed using the DEB or RPM packages then the plugin has to be installed using the root user. Otherwise you can install the plugin as the user that owns all of the Elasticsearch files.
- In the case of DEB or RPM package installation, it is important to check the permissions of the plugins directory after you install it. You can update the permission if it has been modified using the following command:
chown -R elasticsearch:elasticsearch path_to_plugin_directory
- If your Elasticsearch nodes are running in a private subnet without internet access, you cannot install a plugin directly. In this case, you can simply download the plugins and copy the files inside the plugins directory of the Elasticsearch installation path on every node. The node has to be restarted in this case as well.
Log Context
Log “Http client did not trust this server’s certificate; closing connection {}” classname is SecurityNetty4HttpServerTransport.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
} else if (isReceivedCertificateUnknownException(cause)) {
if (logger.isTraceEnabled()) {
logger.trace(new ParameterizedMessage("http client did not trust server's certificate; closing connection {}";
ctx.channel()); cause);
} else {
logger.warn("http client did not trust this server's certificate; closing connection {}"; ctx.channel());
}
ctx.channel().close();
} else {
super.exceptionCaught(ctx; cause);
}
