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https://issues.apache.org/jira/browse/ZOOKEEPER-2691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15870905#comment-15870905
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ASF GitHub Bot commented on ZOOKEEPER-2691:
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Github user afine commented on the issue:
https://github.com/apache/zookeeper/pull/173
sure, one is on the client and one is on the server but I do not think that
means the problem is inherently different.
I think it would be fair to say that both pr's revolve around what to do
when the answer we select from dns is not one that we could use (they both
revolve around calls to `InetAddress.getAllByName`). This patch description is
framed in a way where we are assuming there is a list of possible ip addresses
for some hostname and we just need to find one that is working. Nevertheless,
this patch should work when the address the hostname resolves to changes
entirely.
Likewise, ZOOKEEPER-2184 should handle the "first record doesn't work"
issue you are solving here.
I think it may be valuable to have some shared code that effectively deals
with mapping ip addresses to hostnames.
After an offline discussion with @hanm we concluded that this may be good
to look into after both 2691 and 2184 are merged in.
> 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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