Elasticsearch in Go, Err: "the client noticed that the server is not Elasticsearch and we do not support this unknown product"

I'm working on using Elasticsearch in Go, I followed this guide: https://developer.okta.com/blog/2021/04/23/elasticsearch-go-developers-guide

I set up Elastic with docker.
Verify that Elasticsearch is running:

$ curl http://localhost:9200
{
  "name" : "0e9e2916eca5",
  "cluster_name" : "docker-cluster",
  "cluster_uuid" : "jh8PVKNASpO3uK87Jzoq6Q",
  "version" : {
    "number" : "7.5.2",
    "build_flavor" : "default",
    "build_type" : "docker",
    "build_hash" : "8bec50e1e0ad29dad5653712cf3bb580cd1afcdf",
    "build_date" : "2020-01-15T12:11:52.313576Z",
    "build_snapshot" : false,
    "lucene_version" : "8.3.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}

Also from the browser seems fine.

Next I set up a sample Go program just to test it out:

package main

import (
	"testing"
	"github.com/elastic/go-elasticsearch/v8"
)

func Test_elastic(t *testing.T) {

	es, err := elasticsearch.NewDefaultClient()
    if err != nil {
   	 panic(err)
    }

    res, err := es.Info()
    if err != nil {
   	 panic(err)
    }
    defer res.Body.Close()
}

but res returns with err:

> "the client noticed that the server is not Elasticsearch and we do not
> support this unknown product"

Digging in the code I see it verifies the response by looking for header.Get("X-Elastic-Product") == "Elasticsearch".

I have no idea why it's not working and I couldn't find any reference for this error online... would appreciate any input on this.

You are using v8 of the elasticsearch client, but v7.5.2 of elasticsearch itself. You need to use the library version corresponding to the elasticsearch version, like github.com/elastic/go-elasticsearch/v7. It seems that the check for the header was only added recently in order to not make the library work with any forks.

Adding to @izolight's answer, You can use any old version that works for you and where the validation is not added. The go-elasticsearch v7.13.1 and v6.8.10 are the latest versions without the product check.

go.mod:

	github.com/elastic/go-elasticsearch/v7 v7.13.1
    github.com/elastic/go-elasticsearch/v6 v6.8.10

sample.go:

package main

import (
    "testing"
    "github.com/elastic/go-elasticsearch/v7"
)

func Test_elastic(t *testing.T) {

    es, err := elasticsearch.NewDefaultClient()
    if err != nil {
     panic(err)
    }

    res, err := es.Info()
    if err != nil {
     panic(err)
    }
    defer res.Body.Close()
}

Off-Topic:

By doing this, the Elasticsearch forks like OpenSearch won't be able to use go-elasticsearch client. Same product checks are added to other client libraries, say elastic/elasticsearch-py.

In response, Amazon has planned to fork the Client libraries too and maintain them as like OpenSearch.

• Keeping clients of OpenSearch and Elasticsearch compatible with open source

Just a side note that if you are writing tests against ES and running into this issue when following the recommendation to use a mock for a custom http.Transport, make sure your mock response includes the headers, as seen at https://github.com/elastic/go-elasticsearch/blob/main/elasticsearch_internal_test.go#L53