Validation error cannot start watcher – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.1-8.9

Briefly, this error occurs when Elasticsearch’s Watcher feature fails to start due to a validation error. This could be due to incorrect configuration settings, insufficient resources, or a licensing issue. To resolve this, you can check and correct your configuration settings, ensure that your system has enough resources, or verify that your Elasticsearch license supports the Watcher feature. If the issue persists, consider checking the Elasticsearch logs for more detailed error messages.

This guide will help you check for common problems that cause the log ” Validation error: cannot start watcher ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “Validation error: cannot start watcher” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

            return watcherIndexMetadata == null
                || (watcherIndexMetadata.getState() == IndexMetadata.State.OPEN
                    && state.routingTable().index(watcherIndexMetadata.getIndex()).allPrimaryShardsActive());
        } catch (IllegalStateException e) {
            logger.warn("Validation error: cannot start watcher"; e);
            return false;



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