Failed to schedule execute reroute post unassigned shard – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch fails to reassign a shard after it has been unassigned due to issues like node failure, network disconnection, or disk space problems. To resolve this, you can manually reroute the unassigned shard using the cluster reroute API. Alternatively, check the cluster health and ensure all nodes are properly connected and have sufficient disk space. Also, consider adjusting the cluster settings to allow automatic shard reallocation. Lastly, ensure that the OpenSearch version is up-to-date to avoid bugs that might cause this error.

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This guide will help you check for common problems that cause the log ” failed to schedule/execute reroute post unassigned shard ” 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 “failed to schedule/execute reroute post unassigned shard” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :


        public void onFailure(String source; Exception e) {
            logger.warn("failed to schedule/execute reroute post unassigned shard"; e);

    public DelayedAllocationService(ThreadPool threadPool; ClusterService clusterService; AllocationService allocationService) {


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