UnknowhHostException 使用 spring-cloud-starter-gateway 和 spring boot 2.4.0 及更高版本答案

【问题标题】：UnknowhHostException using spring-cloud-starter-gateway with spring boot 2.4.0 and aboveUnknowhHostException 使用 spring-cloud-starter-gateway 和 spring boot 2.4.0 及更高版本
【发布时间】：2021-04-13 12:39:27
【问题描述】：

与https://github.com/reactor/reactor-netty/issues/1431相关。

Spring 云网关服务器正常启动，但通过网关的请求失败，并出现以下异常：

java.net.UnknownHostException: failed to resolve 'myserver' after 4 queries
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013)
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ? org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
|_ checkpoint ? org.springframework.cloud.sleuth.instrument.web.TraceWebFilter [DefaultWebFilterChain]
|_ checkpoint ? org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
|_ checkpoint ? HTTP GET "/service/api/applications/123" [ExceptionHandlingWebHandler]
Stack trace:
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013)
at io.netty.resolver.dns.DnsResolveContext.tryToFinishResolve(DnsResolveContext.java:966)
at io.netty.resolver.dns.DnsResolveContext.query(DnsResolveContext.java:414)
at io.netty.resolver.dns.DnsResolveContext.onResponse(DnsResolveContext.java:601)
at io.netty.resolver.dns.DnsResolveContext.access$400(DnsResolveContext.java:63)
at io.netty.resolver.dns.DnsResolveContext$2.operationComplete(DnsResolveContext.java:458)
.....

Works correctly when downgrading spring boot.

【问题讨论】：

标签： spring spring-boot dns spring-cloud-gateway

【解决方案1】：

通过添加以下 bean 定义来修复：

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import io.netty.resolver.DefaultAddressResolverGroup;
import reactor.netty.http.client.HttpClient;

@Configuration
public class TempFixConfig {

    @Bean
    public HttpClient webClient() {
        return HttpClient.create().resolver(DefaultAddressResolverGroup.INSTANCE);
    }
}

【讨论】：

【解决方案2】：

如果你不想改变HttpClient bean的创建逻辑，你可以添加一个HttpClientCustomizer：

import org.springframework.cloud.gateway.config.HttpClientCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import io.netty.resolver.DefaultAddressResolverGroup;
import reactor.netty.http.client.HttpClient;

@Configuration
public class HttpClientResolverFixConfig {

    @Bean
    public HttpClientCustomizer httpClientResolverCustomizer() {
        return new HttpClientCustomizer() {

            @Override
            public HttpClient customize(HttpClient httpClient) {
                return httpClient.resolver(DefaultAddressResolverGroup.INSTANCE);
            }
        };
    }

}

【讨论】：