Unexpected failure during – How to solve related issues

Opster Team

Jan-20, Version: 1.7-8.0

Before you begin reading this guide, we recommend you run Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many errors.

To easily locate the root cause and resolve this issue try AutoOps for Elasticsearch & OpenSearch. It diagnoses problems by analyzing hundreds of metrics collected by a lightweight agent and offers guidance for resolving them.

This guide will help you check for common problems that cause the log ” Unexpected failure during ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: admin and cluster.

Log Context

Log “Unexpected failure during [{}]” classname is TransportClusterHealthAction.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

                         listener.onFailure(new NotMasterException("no longer master. source: [" + source + "]"));

                    public void onFailure(String source; Exception e) {
                        logger.error(() -> new ParameterizedMessage("unexpected failure during [{}]"; source); e);
        } else {


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