偶发性出现：UnknownHostException

【问题】 偶发性出现，最近时间比较频繁： java.net.UnknownHostException: www.xxx.com 的异常。

ping www.xxx.com ping正常没有丢包，但是多个java项目调用接口均出现此问题。

【说明】 ssl：Symantec单域名证书（免费）版 代理web服务器：nginx

【日志】 feign.RetryableException: www.xxx.com executing POST https://www.xxx.com/xxx/handle at feign.FeignException.errorExecuting(FeignException.java:84) at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:113) at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:78) at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103) at com.sun.proxy.$Proxy117.post(Unknown Source) at com.yuqiongtech.ssit.service.impl.FeignClientCaller.post(FeignClientCaller.java:38) at com.yuqiongtech.ssit.xdelay.XdelayReceiver.lambda$get$0(XdelayReceiver.java:56) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: java.net.UnknownHostException: www.xxx.com at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) at java.net.Socket.connect(Socket.java:589) at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:673) at sun.net.NetworkClient.doConnect(NetworkClient.java:175) at sun.net.www.http.HttpClient.openServer(HttpClient.java:463) at sun.net.www.http.HttpClient.openServer(HttpClient.java:558) at sun.net.www.protocol.https.HttpsClient. (HttpsClient.java:264) at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:367) at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191) at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1156) at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1050) at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177) at sun.net.www.protocol.http.HttpURLConnection.getOutputStream0(HttpURLConnection.java:1334) at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1309) at sun.net.www.protocol.https.HttpsURLConnectionImpl.getOutputStream(HttpsURLConnectionImpl.java:259) at feign.Client$Default.convertAndSend(Client.java:124) at feign.Client$Default.execute(Client.java:67) at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:108) ... 8 more