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Why Multiple Elasticsearch Nodes Fail to Form a Cluster: master_not_discovered_exception or NotMasterException and How to Fix It

If you’ve encountered a situation where multiple Elasticsearch nodes fail to automatically form a cluster and the logs show the error: “master_not_discovered_exception”, you are not alone.

The Problem

The root cause is often related to system administrators cloning virtual machines to create multiple Elasticsearch servers. When this happens, every Elasticsearch node ends up with the same node ID, and as a result, the cluster cannot successfully elect a master node.

Verifying the Issue

You can verify this issue by listing all the node IDs with the following command:

GET /_cat/nodes?v&h=id,ip,name&full_id=true

However, since the Elasticsearch cluster hasn’t formed, you need to query each node individually, like this:

curl 192.168.110.111:9200/_cat/nodes?v&h=id,ip,name&full_id=true
curl 192.168.110.112:9200/_cat/nodes?v&h=id,ip,name&full_id=true

The Solution

Elasticsearch requires each node to have a unique node ID. To fix this issue, you need to delete the index data on each node. If Elasticsearch was installed using the RPM package, the index data is usually stored in /var/lib/elasticsearch by default. After deleting the data, restart Elasticsearch, and it will generate a new, unique node ID for each node.

Reference

For further details, check the full article here: https://www.656463.com/wenda/jdbhjrjqNotMasterExceptionqgddxc_359.

发布于

多个Elasticsearch节点无法组成集群，报错master_not_discovered_exception或NotMasterException的原因和解决方法

多个Elasticsearch节点无法自动组成集群，查看日志发现错误信息：“master_not_discovered_exception”。

原因是运维人员通过克隆虚拟机来获得多台Elasticsearch服务器，这样每个Elasticsearch节点都具有相同的节点ID，因此在组成集群时，无法选举出master节点。

这可以通过以下命令进行验证，列出所有节点ID：

GET /_cat/nodes?v&h=id,ip,name&full_id=true

请注意，由于Elasticsearch集群尚未形成，因此需要单独查询每个节点，即： 

curl 192.168.110.111:9200/_cat/nodes?v&h=id,ip,name&full_id=true
curl 192.168.110.112:9200/_cat/nodes?v&h=id,ip,name&full_id=true
......

Elasticsearch节点ID必须是唯一的。要解决这个问题，我们需要删除每个节点上的索引（RPM方式安装的Elasticsearch的索引数据默认位于/var/lib/elasticsearch）。重启Elasticsearch就会重置节点ID。 

参考

https://www.656463.com/wenda/jdbhjrjqNotMasterExceptionqgddxc_359