Failed to apply started shards – 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 allocate shards to nodes in the cluster. This could be due to insufficient resources, network issues, or configuration errors. To resolve this, you can try increasing the resources of your nodes, checking your network connectivity, or reviewing your shard allocation settings. Additionally, ensure that your cluster health is green and that there are no unassigned shards. If the issue persists, consider reindexing your data or increasing the number of nodes in your cluster.

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This guide will help you check for common problems that cause the log ” failed to apply started shards {} ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: shards, cluster, shard.

Log Context

Log “failed to apply started shards {}” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

            ClusterState maybeUpdatedState = currentState;
            try {
                maybeUpdatedState = allocationService.applyStartedShards(currentState; shardRoutingsToBeApplied);
            } catch (Exception e) {
                logger.warn(() -> new ParameterizedMessage("failed to apply started shards {}"; shardRoutingsToBeApplied); e);
                builder.failures(tasksToBeApplied; e);



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