Zookeeper Java客户端连接慢、超时问题Ad-Hoc检查清单
TL;DR排查思路：
[*]首先确认你的设备到zookeeper的连通性是OK的，可通过命令echo srvr | nc HOST 2181，检查是否可以正常打印节点信息。windows用户可以在命令行输入telnet HOST 2181连接后输入srvr然后回车。
[*]若步骤1检查OK，但就是连接慢或者超时，则通过启动进程连接zk期间执行jstack -l <pid>获取线程dump信息进一步分析，若不想一一排查，可尝试下面方法快速试下：
[*]本地配置hosts文件，添加下面条目：127.0.0.1 localhost mbpro.local::1 localhost mbpro.local注意：mbpro.local要替换为hostname命令的输出
[*]启动Java进程时配置系统属性：-Djava.net.preferIPv4Stack=true -Dzookeeper.sasl.client=false
case记录
Zookeeper Java客户端初始化打印日志记录环境信息，卡在InetAddress.getLocalHost().getCanonicalHostName()方法
"ZookeeperServiceUrlProvider-1" #1 prio=5 os_prio=0 tid=0x00000000033b0800 nid=0x432c runnable java.lang.Thread.State: RUNNABLE at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:928) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1323) at java.net.InetAddress.getAllByName0(InetAddress.java:1276) at java.net.InetAddress.getAllByName0(InetAddress.java:1253) at java.net.InetAddress.getHostFromNameService(InetAddress.java:634) at java.net.InetAddress.getCanonicalHostName(InetAddress.java:588) at org.apache.zookeeper.Environment.list(Environment.java:62) at org.apache.zookeeper.Environment.logEnv(Environment.java:98) at org.apache.zookeeper.ZooKeeper.<clinit>(ZooKeeper.java:97) at ...解决方法：本地配置hosts文件，添加下面条目
127.0.0.1 localhost mbpro.local::1 localhost mbpro.local注意：mbpro.local要替换为hostname命令的输出
DNS解析响应慢导致zk客户端SendThread卡住较长时间
"ZookeeperServiceUrlProvider-1-SendThread()@9231" daemon prio=5 tid=0x1b nid=NA waitingjava.lang.Thread.State: WAITING at java.lang.Object.wait(Object.java:-1) at java.lang.Object.wait(Object.java:502) at java.net.InetAddress.checkLookupTable(InetAddress.java:1393) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1310) at java.net.InetAddress.getAllByName0(InetAddress.java:1276) at java.net.InetAddress.getAllByName0(InetAddress.java:1253) at java.net.InetAddress.getHostFromNameService(InetAddress.java:634) at java.net.InetAddress.getHostName(InetAddress.java:559) at java.net.InetAddress.getHostName(InetAddress.java:531) at java.net.InetSocketAddress$InetSocketAddressHolder.getHostName(InetSocketAddress.java:82) at java.net.InetSocketAddress$InetSocketAddressHolder.access$600(InetSocketAddress.java:56) at java.net.InetSocketAddress.getHostName(InetSocketAddress.java:345) at org.apache.zookeeper.ClientCnxn$SendThread.startConnect(ClientCnxn.java:998) at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1060)解决方法：
[*]进一步排查DNS解析响应慢的问题
[*]切换至使用IP地址方式连接
客户端尝试SASL认证方式触发DNS解析，DNS解析响应慢导致超时
"ZookeeperServiceUrlProvider-1-SendThread(HOST:2181)" #34 daemon prio=5 os_prio=0 tid=0x0000024d6f94a000 nid=0xa984 runnable java.lang.Thread.State: RUNNABLE at java.net.Inet4AddressImpl.getHostByAddr(Native Method) at java.net.InetAddress$2.getHostByAddr(InetAddress.java:933) at java.net.InetAddress.getHostFromNameService(InetAddress.java:618) at java.net.InetAddress.getHostName(InetAddress.java:560) at java.net.InetAddress.getHostName(InetAddress.java:532) at java.net.InetSocketAddress$InetSocketAddressHolder.getHostName(InetSocketAddress.java:82) at java.net.InetSocketAddress$InetSocketAddressHolder.access$600(InetSocketAddress.java:56) at java.net.InetSocketAddress.getHostName(InetSocketAddress.java:345) at org.apache.zookeeper.SaslServerPrincipal$WrapperInetSocketAddress.getHostName(SaslServerPrincipal.java:105) at org.apache.zookeeper.SaslServerPrincipal.getServerPrincipal(SaslServerPrincipal.java:59) at org.apache.zookeeper.SaslServerPrincipal.getServerPrincipal(SaslServerPrincipal.java:41) at org.apache.zookeeper.ClientCnxn$SendThread.startConnect(ClientCnxn.java:1161) at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1211) Locked ownable synchronizers: - None解决方法：启动Java进程时配置-Dzookeeper.sasl.client=false禁用SASL（如果你不知道SASL是什么，那你大概率并不需要它）
详见：SASL Client-Server mutual authentication
参考链接
[*]https://stackoverflow.com/a/39698914
关于作者
作者 萧易客 一线深耕消息中间件，RPC框架多年，欢迎评论区或通过邮件交流。
微信公众号: 萧易客
github id: shawyeok
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