偶发java.net.UnknownHostException

一、问题描述

现通过公网与某机构联调测试，环境、服务、网络都未变动的情况下，偶发性出现域名解析错误问题。

java.net.UnknownHostException: open-test.nbcb.com.cn
    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:666)
    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.<init>(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.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:162)

二、排查分析

UnknownHostException-域名解析异常。

ping域名正常

[root@osb39 info]# ping open-test.nbcb.com.cn
PING open-test.nbcb.com.cn (1x3.1x6.1x8.8) 56(84) bytes of data.

telnet端口正常

[root@osb39 info]# telnet open-test.nbcb.com.cn 443
Trying 1x3.1x6.1x8.8...
Connected to open-test.nbcb.com.cn.
Escape character is '^]'.

curl偶发出现解析失败

三、问题解决

一般来讲，域名解析失败必然和DNS有关。
联系网络同事修改DNS（cat /etc/resolv.conf）配置后发现问题依旧存在。
后直接写死地址到hosts配置中，

vi /etc/hosts
1x3.1x6.1x8.8 open-test.nbcb.com.cn

偶发解析异常的根本原因暂未查明。本篇主要记录排查过程及解决方式。