How to let then client reuse http connection?

Elasticsearch version: V8.11.0 go-elasticsearch/v8

I have successfully set up Elasticsearch on my local machine using Docker. To create a client, I have set the MaxIdleConnsPerHost parameter to 10. Now, I am indexing documents using the bulk API. Since there are a large number of documents, it may take some time to complete the process.

func NewClientV8(ctx context.Context) *elasticsearch.Client {
    cert, err := ioutil.ReadFile("http_ca.crt")
    if err != nil {
        log.Fatalf("Failed to load certificate: %v", err)
    }

    certPool := x509.NewCertPool()
    certPool.AppendCertsFromPEM(cert)

    cfg := elasticsearch.Config{
        Addresses: []string{
            "https://localhost:9200",
        },
        Username: "elastic",
        Password: "bghCDHWKJknLrkr+8ZMF",
        Transport: &http.Transport{
            MaxIdleConnsPerHost: 20,
            TLSClientConfig: &tls.Config{
                RootCAs: certPool,
            },
        },
    }

    es, err := elasticsearch.NewClient(cfg)
    if err != nil {
        log.Fatalf("Error creating the client: %s", err)
        return es
    }

    res, err := es.Info()
    if err != nil {
        log.Fatalf("Error getting response: %s", err)
    }
    defer res.Body.Close()

    log.Println(res)
    return es
}

func (*ES8) Bulk(ctx context.Context, docs []BulkRequest) error {

    bulkRequestBody := strings.Builder{}
    for _, doc := range docs {
        metaData := fmt.Sprintf(`{ "index" : { "_index" : "%s", "_id" : "%s" } }%s`, index, doc.Id, "\n")
        docData, err := json.Marshal(doc.Doc)
        if err != nil {
            log.Printf("Error marshaling document: %v", err)
            continue
        }
        bulkRequestBody.WriteString(metaData)
        bulkRequestBody.Write(docData)
        bulkRequestBody.WriteString("\n")
    }

    // Send the bulk request
    req := esapi.BulkRequest{
        Index:   index,
        Body:    strings.NewReader(bulkRequestBody.String()),
        Refresh: "true",
        Pretty:  true,
    }
    res, err := req.Do(context.Background(), es)
    if err != nil {
        log.Fatalf("Error performing bulk request: %s", err)
        return err
    }
    defer res.Body.Close()

    // if res.IsError() {
    //  log.Printf("Error[%s]: %s", res.Status(), res.String())
    // } else {
    //  log.Println("Bulk insert successful", res.String())
    // }
    return nil
}

Initially, it worked perfectly fine. However, at the end, I encountered an error message: Error performing bulk request: read tcp 127.0.0.1:50989->127.0.0.1:9200: read: connection reset by peer. And i found the http connections is increasing at the process.

Does the client reuse the http connections default? If it does not, how could let it reuse? Thanks for your reply!

elastic / go-elasticsearch

How to let then client reuse http connection? #781