App.java

import com.linecorp.armeria.client.ClientFactory;
import com.linecorp.armeria.client.ClientFactoryBuilder;
import com.linecorp.armeria.client.HttpClient;
import com.linecorp.armeria.client.HttpClientBuilder;
import com.linecorp.armeria.client.metric.MetricCollectingClient;
import com.linecorp.armeria.common.AggregatedHttpMessage;
import com.linecorp.armeria.common.HttpResponse;
import com.linecorp.armeria.common.SessionProtocol;
import com.linecorp.armeria.common.metric.MeterIdPrefixFunction;
import com.linecorp.armeria.common.metric.PrometheusMeterRegistries;
import com.linecorp.armeria.server.HttpService;
import com.linecorp.armeria.server.ServerBuilder;
import com.linecorp.armeria.server.metric.MetricCollectingService;
import com.linecorp.armeria.server.metric.PrometheusExpositionService;

import io.micrometer.core.instrument.MeterRegistry;
import io.prometheus.client.CollectorRegistry;

public class App {
    public static void main(String[] args) {
        CollectorRegistry collectorRegistry = new CollectorRegistry();
        MeterRegistry meterRegistry = PrometheusMeterRegistries.newRegistry(collectorRegistry);
        ClientFactory clientFactory = new ClientFactoryBuilder().meterRegistry(meterRegistry).build();
        HttpClient httpClient = new HttpClientBuilder("http://127.0.0.1:9998")
                .factory(clientFactory)
                .decorator(MetricCollectingClient.newDecorator(MeterIdPrefixFunction.ofDefault("client")))
                .build();
        new ServerBuilder()
                .port(20080, SessionProtocol.HTTP)
                .service("/", ((HttpService) (ctx, req) ->
                        HttpResponse.from(req.aggregate()
                                             .thenComposeAsync(message -> {
                                                 return httpClient
                                                         .execute(message.toHttpRequest())
                                                         .aggregate()
                                                         .thenApply(AggregatedHttpMessage::toHttpResponse);
                                             })))
                        .decorate(MetricCollectingService.newDecorator(MeterIdPrefixFunction.ofDefault("server")
                        )))
                .meterRegistry(meterRegistry)
                .service("/dump", new PrometheusExpositionService(collectorRegistry))
                .build()
                .start()
                .join();
    }
}