返回给 Java 程序和在 tomcat 中运行的代码的 IP 地址不正确

Question

OS： Red Hat Enterprise Linux Server release 6.6 (Santiago)在tomcat中运行的Java jdk1.8.0_45独立程序和代码为少数主机名返回错误的IP地址。正确的 IP 由同一台计算机上的 dig 和 nslookup 返回。使用 strace -s 2048 -o strace_log -ff 不会产生任何有用的故障排除信息。使用 -Dsun.net.spi.nameservice.nameservers=8.8.8.8 或本地 DNS 服务器(由 nslookup 和 dig 使用(返回相同的错误地址。

[INFO]  sun.net.InetAddressCachePolicy.get() = 30
[INFO]  sun.net.spi.nameservice.provider.1 = null
[INFO]  sun.net.spi.nameservice.nameservers = 8.8.8.8

将 dnsjava 与 -Dsun.net.spi.nameservice.provider.1="dns,dnsjava" 一起使用会返回正确的 IP 地址。

如何检查 java 实际使用的名称服务器？或者还有更多的故障排除技术？

谢谢

Test.sh

#!/bin/sh
HOST=REMOVED
NAMESERVER=LOCAL_NAME_SERVER_IP
NAMESERVER=8.8.8.8
# -Djava.net.preferIPv4Stack=true  #-Dsun.net.spi.nameservice.nameservers=$NAMESERVER 
# -javaagent:dnslog.jar 
# -Dsun.net.spi.nameservice.provider.1="dns,dnsjava" 
# -cp ".:./dnsjava-2.1.8.jar" 
javac Test.java
rm strace_log.*
strace -s 2048 -o strace_log -ff java 
     -Djava.net.preferIPv4Stack=true 
     -Dsun.net.spi.nameservice.nameservers=$NAMESERVER 
     Test https://$HOST
dig $HOST > ${HOST}_dig.txt
nslookup $HOST > ${HOST}_nslookup.txt
java -cp "./dnsjava-2.1.8.jar" dig $HOST > ${HOST}_dnsjava.txt

测试.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.*;
import java.util.logging.*;
public class Test extends Formatter {
  public static void main(String[] args) throws Exception {
    Logger log = Logger.getLogger(Test.class.getName());
    log.setUseParentHandlers(false);
    ConsoleHandler handler = new ConsoleHandler();
    handler.setFormatter(new Test());
    log.addHandler(handler);
    log.info("sun.net.InetAddressCachePolicy.get() = " + sun.net.InetAddressCachePolicy.get());
    log.info("sun.net.spi.nameservice.provider.1 = " + System.getProperty("sun.net.spi.nameservice.provider.1"));
    log.info("sun.net.spi.nameservice.nameservers = " + System.getProperty("sun.net.spi.nameservice.nameservers"));
    try {
      if (args.length != 1 && args.length != 2) {
        log.warning("Usage: java Test <https://address.server.edu> [timeout]");
        return;
      }
      log.info("Received host address " + args[0]);
      URL constructedUrl = new URL(args[0]);
      String host = constructedUrl.getHost();
      InetAddress address = InetAddress.getByName(host);
      String ip = address.getHostAddress();
      log.info("Host = " + args[0] + " IP = " + ip);
      InetAddress Address = InetAddress.getLocalHost();
      log.info("InetAddress.getLocalHost() = " + Address);
      log.info("InetAddress.getCanonicalHostName() = " + Address.getCanonicalHostName());
      InetAddress SW[] = InetAddress.getAllByName(host);
      for (int i=0; i < SW.length; i++) {
        log.info("getAllByName[" + i + "] = " + SW[i]);
      }
      URLConnection conn = constructedUrl.openConnection();
      if (args.length == 2) {
        conn.setConnectTimeout(Integer.valueOf(args[1]) * 1000);
      } else {
        conn.setConnectTimeout(5000);
      }
      log.info("Setting connection timeout to " + conn.getConnectTimeout() / 1000 + " second(s).");
      log.info("Trying to connect to " + args[0]);
      InputStreamReader reader = new InputStreamReader(conn.getInputStream(), "UTF-8");
      BufferedReader in = new BufferedReader(reader);
      in.readLine();
      in.close();
      reader.close();
      log.info("Great! It worked.");
    } catch (Exception e) {
      log.info("Could not connect to the host address " + args[0]);
      log.info("The error is: " + e.getMessage());
      log.info("Here are the details:");
      log.log(Level.SEVERE, e.getMessage(), e);
      throw new RuntimeException(e);
    }
  }
  public String format(LogRecord record) {
    StringBuffer sb = new StringBuffer();
    sb.append("[");
    sb.append(record.getLevel().getName());
    sb.append("]t");
    sb.append(formatMessage(record));
    sb.append("n");
    return sb.toString();
  }
}

Answer 1

此问题已通过重新启动 nscd 守护程序得到解决。它有点挂起，因为有许多nscd -i hosts处理正在运行，但它仍然响应来自应用程序的查询。这可能解释了为什么 DNS TTL 没有得到认可。