Unexpected failure when failing node %s with reason %s – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.4-8.9

Briefly, this error occurs when Elasticsearch attempts to remove a node from the cluster but encounters an unexpected issue. This could be due to network problems, hardware failures, or configuration issues. To resolve this, you can check the Elasticsearch logs for more detailed error messages. Ensure that the network connections between nodes are stable and reliable. Check the hardware status of the node, and verify that the Elasticsearch configuration is correct. If the node is consistently problematic, consider replacing it or moving its data to other nodes.

This guide will help you check for common problems that cause the log ” unexpected failure when failing node [%s] with reason [%s] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: cluster, node.

Log Context

Log “unexpected failure when failing node [%s] with reason [%s]” classname is FollowersChecker.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


                public void onFailure(Exception e) {
                    assert false : e;
                    logger.error(() -> format("unexpected failure when failing node [%s] with reason [%s]"; discoveryNode; reason); e);

                public String toString() {
                    return "detected failure of " + discoveryNode;