UnknownHostException: nacos-provider #2138

Why does the 2021.1 version of "spring-cloud-starter-alibaba-nacos-discovery" cannot find the ribbon, which results in a prompt that the provider cannot be obtained in "this.getLoadBalancer(serviceId)"

version:

        <spring-boot.version>2.4.2</spring-boot.version>
        <spring-cloud.version>2020.0.3</spring-cloud.version>
        <spring-cloud-alibaba.version>2021.1</spring-cloud-alibaba.version>

error:

java.net.UnknownHostException: nacos-provider
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) ~[na:1.8.0_211]
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) ~[na:1.8.0_211]
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_211]
    at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_211]
    at java.net.Socket.connect(Socket.java:538) ~[na:1.8.0_211]
    at sun.net.NetworkClient.doConnect(NetworkClient.java:180) ~[na:1.8.0_211]
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:463) ~[na:1.8.0_211]
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:558) ~[na:1.8.0_211]
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:242) ~[na:1.8.0_211]
    at sun.net.www.http.HttpClient.New(HttpClient.java:339) ~[na:1.8.0_211]
    at sun.net.www.http.HttpClient.New(HttpClient.java:357) ~[na:1.8.0_211]
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1220) ~[na:1.8.0_211]
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1156) ~[na:1.8.0_211]
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1050) ~[na:1.8.0_211]
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:984) ~[na:1.8.0_211]
    at org.springframework.http.client.SimpleBufferingClientHttpRequest.executeInternal(SimpleBufferingClientHttpRequest.java:76) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:66) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:775) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:710) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:333) ~[spring-web-5.3.3.jar:5.3.3]
    at cn.sky.cloud.alibaba.controller.TestController.sayHello(TestController.java:34) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_211]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_211]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_211]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_211]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.3.jar:5.3.3]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.3.jar:5.3.3]

There is no problem when using the following versions：

        <spring-boot.version>2.3.2</spring-boot.version>
        <spring-cloud.version>Hoxton.SR8</spring-cloud.version>
        <spring-cloud-alibaba.version>2.2.5.RELEASE</spring-cloud-alibaba.version>

已经解决了。 2020版本就已经不再使用netflix，自然也就没有了ribbon。怎么办？使用Spring Cloud Load Balancer代替

1. pom.xml add dependency:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-loadbalancer</artifactId>
</dependency>

1. application.yml下增加禁用ribbon配置

spring:
  application:
    name: nacos-client
  cloud:
    loadbalancer:
      ribbon:
        enabled: false

这里我的各个版本是：