Failed to apply started shards – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-8.2

Briefly, this error occurs when Elasticsearch is unable to allocate shards to nodes in the cluster due to issues like insufficient resources, network connectivity problems, or configuration errors. To resolve this, you can try increasing the system resources, checking the network connectivity between nodes, or reviewing the shard allocation settings. Also, ensure that the cluster health status is green and not red or yellow, which indicates problems. If the issue persists, you may need to reindex your data or even restart the Elasticsearch cluster.

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 Elasticsearch concepts: shards, cluster, shard.

Log Context

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

                for (final var taskContext : tasksToBeApplied) {
            } catch (Exception e) {
                logger.warn(() -> new ParameterizedMessage("failed to apply started shards {}"; shardRoutingsToBeApplied); e);
                for (final var taskContext : tasksToBeApplied) {


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