Can t send mapping refresh for no master known – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-1.3

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Briefly, this error occurs when OpenSearch cluster loses its master node, which is responsible for managing cluster-wide changes like creating or deleting indices. This could be due to network issues, heavy load, or configuration problems. To resolve this, ensure that your cluster has enough master-eligible nodes and they can communicate with each other. Check your network settings and configurations. Also, monitor your cluster’s health and load to prevent such issues. If the problem persists, consider increasing the election timeout or adjusting the discovery settings.

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This guide will help you check for common problems that cause the log ” can’t send mapping refresh for [{}]; no master known. ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: master, cluster, index, mapping, refresh.

Log Context

Log “can’t send mapping refresh for [{}]; no master known.” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :


    public void nodeMappingRefresh(final DiscoveryNode masterNode; final NodeMappingRefreshRequest request) {
        if (masterNode == null) {
            logger.warn("can't send mapping refresh for [{}]; no master known."; request.index());
        transportService.sendRequest(masterNode; ACTION_NAME; request; EmptyTransportResponseHandler.INSTANCE_SAME);


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