Failing shard with unassigned info – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when a shard in OpenSearch fails to assign, possibly due to issues like node failure, insufficient disk space, or network problems. To resolve this, you can try the following: 1) Check the cluster health and identify the unassigned shards. 2) Investigate the node logs for any specific issues. 3) Ensure there’s enough disk space and the network is stable. 4) Use the OpenSearch shard allocation API to manually reallocate the unassigned shards. 5) If a specific node is causing the problem, consider removing it and adding a new one.

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This guide will help you check for common problems that cause the log ” {} failing shard {} with unassigned info ({}) ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: routing, cluster, shard.

Log Context

Log “{} failing shard {} with unassigned info ({})” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

            : "shard routing to fail does not exist in routing table; expected: "
                + failedShard
                + " but was: "
                + getByAllocationId(failedShard.shardId(); failedShard.allocationId().getId());

        logger.debug("{} failing shard {} with unassigned info ({})"; failedShard.shardId(); failedShard; unassignedInfo.shortSummary());

        // if this is a primary; fail initializing replicas first (otherwise we move RoutingNodes into an inconsistent state)
        if (failedShard.primary()) {
            List assignedShards = assignedShards(failedShard.shardId());
            if (assignedShards.isEmpty() == false) {


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