How To Solve Issues Related to Log – No nodes to set; nodes will be updated at the next sniffing round

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Last update: Jan-20

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Troubleshooting Background – start here to get the full picture       
Related Issues – selected resources on related issues  
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Troubleshooting background

To troubleshoot Elasticsearch log “No nodes to set; nodes will be updated at the next sniffing round” it’s important to know common problems related to Elasticsearch concepts: client. See below-detailed explanations complete with common problems, examples and useful tips.

Elasticsearch Client

What it is

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 it is 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, and many other programming languages are supported by community versions.

Keep your Elasticsearch version and client version in sync.

To avoid surprises, always keep your client version in line with the Elasticsearch version you are using.  Always test client 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 loads balances across all of the appropriate nodes in the cluster.  In small clusters this will normally mean only 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 (eg. through some sort of queueing mechanism) will be better than simply inundating a struggling cluster with repeated requests.

Nodes in Elasticsearch

What it is

Simply explained a node is a single server that is part of a cluster. Each node is assigned with one or more roles, which describes the node responsibility and operations – Data nodes stores the data, and participates in the cluster’s indexing and search capabilities, while master nodes are responsible for managing the cluster activities and storing the cluster state, including the metadata.

While it’s possible to run several Node instances of Elasticsearch on the same hardware, it’s considered a best practice to limit a server to a single running instance of Elasticsearch.

Nodes connect to each other and form a cluster by using a discovery method. 

Roles
Master node

Master nodes are in charge of cluster-wide settings and changes  – deleting or creating indices and fields, adding or removing nodes and allocating shards to nodes. Each cluster has a single master node that is elected from the master eligible nodes using a distributed consensus algorithm and is reelected if the current master node fails.

Coordinator Node (aka client node)

Coordinator Node – is a node that does not hold any configured role. It doesn’t hold data, not part of the master eligible group nor execute ingest pipelines. Coordinator node serves incoming search requests and is acting as the query coordinator – running the query and fetch phases, sending requests to every node which holds a shard being queried. The client node also distributes bulk indexing operations and route queries to shards copies based on the nodes responsiveness.


To help troubleshoot related issues we have gathered selected Q&A from the community and issues from Github , please review the following for further information :

Transportclient Sniffing Issue
discuss.elastic.co/t/transportclient-sniffing-issue/17100

 

Error While Sniffing
discuss.elastic.co/t/error-while-sniffing/180978

 


Log Context

Log ”No nodes to set; nodes will be updated at the next sniffing round” classname is Sniffer.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

<pre class="wp-block-syntaxhighlighter-code">         List<Node> sniffedNodes = nodesSniffer.sniff();
        if (logger.isDebugEnabled()) {
            logger.debug("sniffed nodes: " + sniffedNodes);
        }
        if (sniffedNodes.isEmpty()) {
            logger.warn("no nodes to set; nodes will be updated at the next sniffing round");
        } else {
            restClient.setNodes(sniffedNodes);
        }
    }





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