Unexpected failure while failing shard – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-1.1

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Briefly, this error occurs when OpenSearch encounters an unexpected issue while trying to fail a shard. This could be due to network issues, disk space problems, or corruption in the shard. To resolve this, you can try relocating the shard to another node, checking the disk space and network connectivity, or restoring the shard from a backup. If the shard is corrupt, you may need to delete and recreate it. Always ensure to monitor your cluster health to prevent such issues.

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This guide will help you check for common problems that cause the log ” {} unexpected failure while failing shard [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: shard, cluster.

Log Context

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

                new ClusterStateTaskListener() {
                    public void onFailure(String source; Exception e) {
                        logger.error(() -> new ParameterizedMessage("{} unexpected failure while failing shard [{}]";
                            request.shardId; request); e);
                        try {
                        } catch (Exception channelException) {


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