Unexpected failure applying – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 6.8-6.8

Briefly, this error occurs when Elasticsearch encounters an issue while trying to apply logs of a specific version, in this case, version 6.8. This could be due to a mismatch between the log version and the Elasticsearch version, or due to corrupted logs. To resolve this issue, you can try upgrading your Elasticsearch to match the log version, or check the integrity of your logs and restore them from a backup if necessary. Additionally, ensure that your Elasticsearch cluster has sufficient resources and is not under heavy load, as this could also cause such errors.

This guide will help you check for common problems that cause the log ” Unexpected failure applying [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: discovery.

Log Context

Log “Unexpected failure applying [{}]” classname is ZenDiscovery.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


                public void onFailure(String source; Exception e) {
                    logger.error(() -> new ParameterizedMessage("unexpected failure applying [{}]"; reason); e);
                    try {
                        // TODO: use cluster state uuid instead of full cluster state so that we don't keep reference to CS around
                        // for too long.
                        pendingStatesQueue.markAsFailed(newClusterState; e);
                    } catch (Exception inner) {


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