Reports

RequestConfig comes from org.apache.httpcomponents.client5:httpclient5
So add that library and try.

HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(
    HttpClientBuilder.create()
        .setDefaultRequestConfig(
            RequestConfig.custom().setProtocolUpgradeEnabled(false).build()
        ).build()
    );

Use the above factory in RestTemplate builder

RestTemplate restTemplate = restTemplateBuilder.requestFactory(() -> factory).build();

More discussions about this issue in Istio forum - https://github.com/istio/istio/issues/53239

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