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https://issues.apache.org/jira/browse/ZOOKEEPER-2691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15870904#comment-15870904
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ASF GitHub Bot commented on ZOOKEEPER-2691:
-------------------------------------------
Github user hanm commented on the issue:
https://github.com/apache/zookeeper/pull/173
>> on the surface this pr reminds me of ZOOKEEPER-2184, wondering if some
of the logic can be shared?
I had a chat with @afine offline again about this and I think Abe had a
good point of view of both problems at a higher level - they are not resolving
exact same problem but there is an opportunity that we could do some
refactoring and code sharing regarding effectively map between usable IP and
host names. This improvement could be done later though given the current many
things in flight status to reduce the risk of this PR being stale...
> 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. For
> example, if a machine has two network interfaces: eth0, eth1, say eth0 has
> ip1, eth1 has ip2, the relationship between hostname and the IP addresses is
> set in /etc/hosts. When I "close" the eth0 by command "ifdown eth0", the
> InetAddress.getByName(String hostname) will still return ip1, which is
> 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:
> {code:title=QuorumPeer.java|borderStyle=solid}
> 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);
> }
> }
> }
> {code}
> After my modification:
> {code:title=QuorumPeer.java|borderStyle=solid}
> 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];
> }
> {code}
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