How To Solve Issues Related to Log – Unexpected failure during cluster

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Last update: Dec-19

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Troubleshooting background

To troubleshoot Elasticsearch log “Unexpected failure during cluster” it’s important to know common problems related to Elasticsearch concepts: license, task. See below-detailed explanations complete with common problems, examples and useful tips.

license in Elasticsearch

What is it

Elasticsearch offers various licenses with different sets of features, ranging from Open Source Basic, Gold, Platinum and Enterprise. The default is set to basic. The basic license is a forever free plan but lacks many advanced x-pack features, such as alerts and advanced security. The following parameter is used inside elaticsearch.yml file to set a license type:

xpack.license.self_generated.type: basic

Task in Elasticsearch

What it is

A task is equivalent to an Elasticsearch operation, which can be any request performed on an Elasticsearch cluster. For example, a delete by query request, a search request and so on. Elasticsearch provides a dedicated Task API for the task management which includes various actions, from retrieving the status of current running tasks to canceling any long running task.

Examples
Get all currently running tasks on all nodes of the cluster

Apart from other information, the response of the below request contains task IDs of all the tasks which can be used to get detailed information about the particular task in question.

GET _tasks
GET detailed information of a particular task

clQFAL_VRrmnlRyPsu_p8A:1132678759 is the ID of the task in below request.

GET _tasks/clQFAL_VRrmnlRyPsu_p8A:1132678759
Get all the current tasks running on particular nodes
GET _tasks?nodes=nodeId1,nodeId2
Cancel a long-running task

clQFAL_VRrmnlRyPsu_p8A:1132678759 is the ID of the task in the below request.

POST /_tasks/clQFAL_VRrmnlRyPsu_p8A:1132678759/_cancel?pretty
Notes
  • The Task API will be most useful when you want to investigate the spike of resource utilization in the cluster or want to cancel an operation.

Cluster in Elasticsearch

What is it

In Elasticsearch a cluster is a collection of one or more nodes (servers / VMs). A cluster can consist of an unlimited number of nodes. The cluster provides interface for indexing and storing data and search capability across all of the data which is stored in the data nodes

Each cluster has a single master node that is elected by the master eligible nodes. In cases where the master is not available the other connected master eligible nodes elect a new master. Clusters are identified by a unique name, which defaults to “Elasticsearch”.


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 :

1. Fail To Assign Shards After Restart  

2. No Cluster Health With 2 Nodes      

Github Issue Number 19488


Log Context

Log ”Unexpected failure during cluster” classname is StartBasicClusterTask.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

         }
    }

    
Override
    public void onFailure(String source; 
Nullable Exception e) {
        logger.error(new ParameterizedMessage("unexpected failure during [{}]"; source); e);
        listener.onFailure(e);
    }
}



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