ACK Response – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 2.5-2.7

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Briefly, this error occurs when OpenSearch receives an acknowledgement (ACK) response from a node after a data operation. It indicates that the operation was successful. However, if you’re seeing this error unexpectedly, it could be due to network issues, incorrect configuration, or a bug in your application. To resolve this, you can check your network connection, verify your OpenSearch configuration, or debug your application to find any potential issues. Additionally, ensure that your OpenSearch cluster is healthy and all nodes are functioning properly.

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This guide will help you check for common problems that cause the log ” ACK Response ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: response.

Log Context

Log “ACK Response” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

        final CompletableFuture inProgressIndexNameFuture = new CompletableFuture();
        final TransportResponseHandler acknowledgedResponseHandler = new TransportResponseHandler() {
            public void handleResponse(AcknowledgedResponse response) {
      "ACK Response" + response);

            public void handleException(TransportException exp) {


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