As per the documentation the HttpClientConfigurer code is not reachable therefore UUID in the log trace is not being added.

public class HttpClientConfigurer implements ElasticsearchHttpClientConfigurer {

@Override

public void configure(ElasticsearchHttpClientConfigurationContext context) {

HttpAsyncClientBuilder clientBuilder = context.clientBuilder();

clientBuilder.addInterceptorFirst((HttpRequestInterceptor) (request, context12) -> {

MDC.put("correlationId", UUID.randomUUID().toString());

});

clientBuilder.addInterceptorFirst((HttpResponseInterceptor) (response, context1) -> {

MDC.put("correlationId", UUID.randomUUID().toString());

});

}

}

hibernate.search.backend.client.configurer =class:com.example.configuration.HttpClientConfigurer

Note : MDC - > A Mapped Diagnostic Context, or MDC in short, is an instrument for distinguishing interleaved log output from different sources. Log output is typically interleaved when a server handles multiple clients near-simultaneously.
MDC.put("correlationId", UUID.randomUUID().toString());
adds the correlationId UUID to the logging context.

Main Goal is to generate logs with UUID for better tracing