Exception caught on transport layer thread= – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-7.15

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Briefly, this error occurs when there is a communication issue between Elasticsearch nodes, often due to network problems, firewall restrictions, or incorrect configuration. To resolve this, ensure all nodes are reachable and there are no network issues. Check firewall settings to allow communication between nodes. Verify the configuration settings, particularly the ‘transport’ and ‘http’ settings. If the issue persists, consider increasing the timeout settings or checking for any hardware issues.

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This guide will help you check for common problems that cause the log ” exception caught on transport layer [thread={}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugins.

Log Context

Log “exception caught on transport layer [thread={}]” classname is NioGroupFactory.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

            return new WrappedNioGroup(refCountedGroup);

    private void onException(Exception exception) {
        logger.warn(new ParameterizedMessage("exception caught on transport layer [thread={}]"; Thread.currentThread().getName());

    private static class RefCountedNioGroup extends AbstractRefCounted implements NioGroup {


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