How To Solve Issues Related to Log – Cannot start plugin due to incorrect Lucene version plugin . node .

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Updated: Feb-20

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Troubleshooting background

To troubleshoot Elasticsearch log “Cannot start plugin due to incorrect Lucene version plugin . node .” it’s important to understand common problems related to Elasticsearch concepts: lucene, node, plugin, plugins. See detailed explanations below complete with common problems, examples and useful tips.

Lucene and Elasticsearch

What it is 

Lucene or Apache Lucene is an open-source Java library used as a search engine. Elasticsearch is built on top of Lucene. 

Elasticsearch converts Lucene into a distributed system/search engine for scaling horizontally. Elasticsearch also provides other features like thread-pool, queues, node/cluster monitoring API, data monitoring API, Cluster management, etc. In short , Elasticsearch extends Lucene and provides additional features in addition to it.

Elasticsearch hosts data on data nodes. Each data node hosts one or more indices , and each index is divided into shards with each shard holding part of the index data. From technical and operative perspectives, each shard created in Elasticsearch is a separate Lucene instance or process. Therefore, this concept is of significant importance when attempting to understand elasticsearch internals , indices and shards.

Notes and Good Things to Know:
  • When an index is created in ElasticSearch it is divided into one or more primary shards for scaling the data and splitting it into multiple nodes/instances. The concept of Lucene is relevant here when you are going to decide the number of shards for your index. Too many shards will result in too many Lucene instances, which will consume resources and damage performance.

  • It takes proper planning to decide the number of primary shards for your index , taking into account the index size , max growth , and the number of data nodes.

  • Previous versions of Elasticsearch defaulted to creating five shards per index. Starting with 7.0.0, the default is now one shard per index.

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.

Plugin in Elasticsearch

What it is

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 the instructions for the plugin usage
sudo bin/elasticsearch-plugin -h
  • Installing S3 plugin using URL 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 path
sudo bin/elasticsearch-plugin install file:///path/to/plugin.zip

Notes:
  • Plugins are installed and removed using the elasticsearch-plugin script, which ships as a part of 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 Problems:
  • Managing permission issues during and after plugin installation is the most common problem. If Elasticsearch was installed using the deb or rpm package then the plugin has to be installed using the root user, or else you can install the plugin as the user that owns all of the Elasticsearch files.
  • In case of deb or rpm package installation, it is important to check the permission of the plugins directory after plugin installation and 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 at once 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.

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 :

 

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Log Context

Log ”cannot start plugin due to incorrect Lucene version: plugin [{}]; node [{}].” classname is PluginsService.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

             }
        } catch (Throwable t) {
            // We don't have the expected version... Let's fail after.
            logger.debug("exception raised while checking plugin Lucene version."; t);
        }
        logger.error("cannot start plugin due to incorrect Lucene version: plugin [{}]; node [{}].";
                luceneVersion; Constants.LUCENE_MAIN_VERSION);
        return false;
    }
}







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