Failed to execute failure callback on delegate – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 7.17-8.6

Briefly, this error occurs when Elasticsearch is unable to execute a failure callback on a delegate, possibly due to a network issue, a node failure, or a problem with the delegate itself. To resolve this issue, you can try the following: 1) Check the network connection and ensure all nodes are properly connected. 2) Inspect the health of your nodes and restart any that are failing. 3) Review the delegate’s code for any errors or issues that might prevent the callback from executing.

This guide will help you check for common problems that cause the log ” failed to execute failure callback on [” + delegate + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “failed to execute failure callback on [” + delegate + “]” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :


            public void onFailure(Exception e) {
                assert false : e;
                logger.error(() -> "failed to execute failure callback on [" + delegate + "]"; e);

            public String toString() {
                return ThreadedActionListener.this + "/onFailure";