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

Opster Team

Aug-23, Version: 6.8-8.9

Briefly, this error occurs when Elasticsearch is unable to schedule a reroute after a shard becomes unassigned. This could be due to a lack of resources, network issues, or configuration errors. To resolve this issue, you can try the following: 1) Check and optimize your cluster’s resources, ensuring there’s enough disk space and memory. 2) Verify your network connectivity and firewall settings. 3) Review your Elasticsearch configuration for any errors, particularly in shard allocation settings. 4) Restart your Elasticsearch nodes to clear any temporary issues.

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 Elasticsearch concepts: routing, cluster, shard.

Log Context

Log “failed to schedule/execute reroute post unassigned shard” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


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

    @SuppressForbidden(reason = "legacy usage of unbatched task") // TODO add support for batching here
    private void submitUnbatchedTask(@SuppressWarnings("SameParameterValue") String source; ClusterStateUpdateTask task) {


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