Leader check from unknown node – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7-7.4

Briefly, this error occurs when a node in an Elasticsearch cluster receives a leader check request from a node it doesn’t recognize. This could be due to a misconfiguration in the cluster settings or a network issue. To resolve this, you can check the cluster’s configuration and ensure all nodes are correctly set up and networked. Also, verify that the unknown node is not a leftover from a previous configuration. If it is, remove it from the cluster. Additionally, ensure that the Elasticsearch version is the same across all nodes to prevent compatibility issues.

This guide will help you check for common problems that cause the log ” leader check from unknown node ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: cluster, node.

Log Context

Log “leader check from unknown node” class name is LeaderChecker.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 if (discoveryNodes.isLocalNodeElectedMaster() == false) {
 logger.debug("non-master handling {}"; request);
 throw new CoordinationStateRejectedException("non-leader rejecting leader check");
 } else if (discoveryNodes.nodeExists(request.getSender()) == false) {
 logger.debug("leader check from unknown node: {}"; request);
 throw new CoordinationStateRejectedException("leader check from unknown node");
 } else {
 logger.trace("handling {}"; request);


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