Unexpected failure during – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch encounters an unexpected issue during a specific operation, denoted by [{}]. This could be due to a variety of reasons such as incorrect configurations, insufficient resources, or network issues. To resolve this, you can start by checking the OpenSearch logs for more detailed error messages. Ensure that your configurations are correct and that your system has enough resources (CPU, memory, disk space). If it’s a network issue, verify your network settings and connectivity. Also, consider upgrading OpenSearch if you’re using an outdated version.

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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 OpenSearch concepts: cluster.

Log Context

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

        return ClusterState.builder(currentState).nodes(remainingNodesBuilder).build();

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

    public void onNoLongerClusterManager(String source) {
        logger.debug("no longer cluster-manager while processing node removal [{}]"; source);


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