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From "JiangJiafu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-2691) recreateSocketAddresses may recreate the unreachable IP address
Date Fri, 10 Feb 2017 11:09:41 GMT
JiangJiafu created ZOOKEEPER-2691:
-------------------------------------

             Summary: recreateSocketAddresses may recreate the unreachable IP address
                 Key: ZOOKEEPER-2691
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2691
             Project: ZooKeeper
          Issue Type: Bug
    Affects Versions: 3.4.8
         Environment: Centos6.5
Java8
ZooKeeper3.4.8
            Reporter: JiangJiafu
            Priority: Minor


The QuorumPeer$QuorumServer.recreateSocketAddress()  is used to resolved the hostname to a
new IP address(InetAddress) when any exception happens to the socket. It will be very useful
when a hostname can be resolved to more than one IP address.
But the problem is Java API InetAddress.getByName(String hostname) will always return the
first IP address when the hostname can be resolved to more than one IP address, and the first
IP address may be unreachable forever. So I think it will be better to check the IP address
by InetAddress.isReachable(long) and choose the reachable IP address. 

I have modified the ZooKeeper source code, and test the new code in my own environment, and
it can work very well when I turn down some network interfaces using "ifdown" command.

The original code is:
{quote}
        public void recreateSocketAddresses() {
            InetAddress address = null;
            try {
                address = InetAddress.getByName(this.hostname);
                LOG.info("Resolved hostname: {} to address: {}", this.hostname, address);
                this.addr = new InetSocketAddress(address, this.port);
                if (this.electionPort > 0){
                    this.electionAddr = new InetSocketAddress(address, this.electionPort);
                }
            } catch (UnknownHostException ex) {
                LOG.warn("Failed to resolve address: {}", this.hostname, ex);
                // Have we succeeded in the past?
                if (this.addr != null) {
                    // Yes, previously the lookup succeeded. Leave things as they are
                    return;
                }
                // The hostname has never resolved. Create our InetSocketAddress(es) as unresolved
                this.addr = InetSocketAddress.createUnresolved(this.hostname, this.port);
                if (this.electionPort > 0){
                    this.electionAddr = InetSocketAddress.createUnresolved(this.hostname,
                                                                           this.electionPort);
                }
            }
        }
{quote}

After my modification:
{quote}
        public void recreateSocketAddresses() {
            InetAddress address = null;
            try {
                address = getReachableAddress(this.hostname);
                LOG.info("Resolved hostname: {} to address: {}", this.hostname, address);
                this.addr = new InetSocketAddress(address, this.port);
                if (this.electionPort > 0){
                    this.electionAddr = new InetSocketAddress(address, this.electionPort);
                }
            } catch (UnknownHostException ex) {
                LOG.warn("Failed to resolve address: {}", this.hostname, ex);
                // Have we succeeded in the past?
                if (this.addr != null) {
                    // Yes, previously the lookup succeeded. Leave things as they are
                    return;
                }
                // The hostname has never resolved. Create our InetSocketAddress(es) as unresolved
                this.addr = InetSocketAddress.createUnresolved(this.hostname, this.port);
                if (this.electionPort > 0){
                    this.electionAddr = InetSocketAddress.createUnresolved(this.hostname,
                                                                           this.electionPort);
                }
            }
        }

        public InetAddress getReachableAddress(String hostname) throws UnknownHostException
{
            InetAddress[] addresses = InetAddress.getAllByName(hostname);
            for (InetAddress a : addresses) {
                try {
                    if (a.isReachable(5000)) {
                        return a;
                    } 
                } catch (IOException e) {
                    LOG.warn("IP address {} is unreachable", a);
                }
            }
            // All the IP address is unreachable, just return the first one.
            return addresses[0];
        }
{quote}



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