Java 程序和 tomcat 中的代码运行返回的 IP 地址不正确

Question

OS: Red Hat Enterprise Linux Server release 6.6 (Santiago) Java jdk1.8.0_45 独立程序和 tomcat 中的代码运行为少数主机名返回了错误的 IP 地址。同一台机器上的 dig 和 nslookup 返回正确的 IP。使用 strace -s 2048 -o strace_log -ff 没有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）returns 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

使用 dnsjava 和 -Dsun.net.spi.nameservice.provider.1="dns,dnsjava" returns 正确的 IP 地址。

如何检查 java 实际使用的名称服务器？或者有更多的故障排除技巧吗？

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

Test.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

问题已通过重新启动 nscd 守护进程解决。它有点挂起，因为有许多 nscd -i hosts 已处理运行，但它仍在响应来自应用程序的查询。这可能解释了为什么 DNS TTL 不受尊重。

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