7.2 Proxying Requests with ProxyHttpClient

A common requirement in Microservice environments is to proxy requests in a Gateway Microservice to other backend Microservices.

The regular HttpClient API is designed around simplifying message exchange and is not designed for proxying requests. For this case, use the ProxyHttpClient, which can be used from a HTTP Server Filter to proxy requests to backend Microservices.

The following example demonstrates rewriting requests under the URI /proxy to the URI /real onto the same server (although in a real environment you generally proxy to another server):

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers;
import io.micronaut.core.util.StringUtils;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.MutableHttpResponse;
import io.micronaut.http.annotation.Filter;
import io.micronaut.http.client.ProxyHttpClient;
import io.micronaut.http.filter.HttpServerFilter;
import io.micronaut.http.filter.OncePerRequestHttpServerFilter;
import io.micronaut.http.filter.ServerFilterChain;
import io.micronaut.runtime.server.EmbeddedServer;
import org.reactivestreams.Publisher;
@Filter("/proxy/**")
public class ProxyFilter implements HttpServerFilter { (1)
    private final ProxyHttpClient client;
    private final EmbeddedServer embeddedServer;
    public ProxyFilter(ProxyHttpClient client,
                       EmbeddedServer embeddedServer) { (2)
        this.client = client;
        this.embeddedServer = embeddedServer;
    }
    @Override
    public Publisher<MutableHttpResponse<?>> doFilter(HttpRequest<?> request,
                                                      ServerFilterChain chain) {
        return Publishers.map(client.proxy( (3)
                request.mutate() (4)
                        .uri(b -> b (5)
                                .scheme("http")
                                .host(embeddedServer.getHost())
                                .port(embeddedServer.getPort())
                                .replacePath(StringUtils.prependUri(
                                        "/real",
                                        request.getPath().substring("/proxy".length())
                                ))
                        )
                        .header("X-My-Request-Header", "XXX") (6)
        ), response -> response.header("X-My-Response-Header", "YYY"));
    }
}

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers
import io.micronaut.core.util.StringUtils
import io.micronaut.http.HttpRequest
import io.micronaut.http.MutableHttpResponse
import io.micronaut.http.annotation.Filter
import io.micronaut.http.client.ProxyHttpClient
import io.micronaut.http.filter.HttpServerFilter
import io.micronaut.http.filter.OncePerRequestHttpServerFilter
import io.micronaut.http.filter.ServerFilterChain
import io.micronaut.http.uri.UriBuilder
import io.micronaut.runtime.server.EmbeddedServer
import org.reactivestreams.Publisher
@Filter("/proxy/**")
class ProxyFilter implements HttpServerFilter { (1)
    private final ProxyHttpClient client
    private final EmbeddedServer embeddedServer
    ProxyFilter(ProxyHttpClient client,
                EmbeddedServer embeddedServer) { (2)
        this.client = client
        this.embeddedServer = embeddedServer
    }
    @Override
    Publisher<MutableHttpResponse<?>> doFilter(HttpRequest<?> request,
                                               ServerFilterChain chain) {
        Publishers.map(client.proxy( (3)
                request.mutate() (4)
                        .uri { UriBuilder b -> (5)
                            b.with {
                                scheme("http")
                                host(embeddedServer.host)
                                port(embeddedServer.port)
                                replacePath(StringUtils.prependUri(
                                        "/real",
                                        request.path.substring("/proxy".length())
                                ))
                            }
                        }
                        .header("X-My-Request-Header", "XXX") (6)
        ), { it.header("X-My-Response-Header", "YYY") })
    }
}

Customizing the Netty pipeline for Logbook

import io.micronaut.core.async.publisher.Publishers
import io.micronaut.core.util.StringUtils
import io.micronaut.http.HttpRequest
import io.micronaut.http.MutableHttpResponse
import io.micronaut.http.annotation.Filter
import io.micronaut.http.client.ProxyHttpClient
import io.micronaut.http.filter.HttpServerFilter
import io.micronaut.http.filter.OncePerRequestHttpServerFilter
import io.micronaut.http.filter.ServerFilterChain
import io.micronaut.http.uri.UriBuilder
import io.micronaut.runtime.server.EmbeddedServer
import org.reactivestreams.Publisher
@Filter("/proxy/**")
class ProxyFilter(
    private val client: ProxyHttpClient, (2)
    private val embeddedServer: EmbeddedServer
) : HttpServerFilter { (1)
    override fun doFilter(request: HttpRequest<*>,
                          chain: ServerFilterChain): Publisher<MutableHttpResponse<*>> {
        return Publishers.map(client.proxy( (3)
            request.mutate() (4)
                .uri { b: UriBuilder -> (5)
                    b.apply {
                        scheme("http")
                        host(embeddedServer.host)
                        port(embeddedServer.port)
                        replacePath(StringUtils.prependUri(
                            "/real",
                            request.path.substring("/proxy".length))
                        )
                    }
                }
                .header("X-My-Request-Header", "XXX") (6)
        ), { response: MutableHttpResponse<*> -> response.header("X-My-Response-Header", "YYY") })
    }
}