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https://issues.apache.org/jira/browse/ZOOKEEPER-2691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15872521#comment-15872521
]
ASF GitHub Bot commented on ZOOKEEPER-2691:
-------------------------------------------
Github user eribeiro commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/173#discussion_r101845264
--- Diff: src/java/main/org/apache/zookeeper/server/quorum/QuorumPeer.java
---
@@ -181,6 +197,33 @@ public void recreateSocketAddresses() {
}
}
+ /**
+ * Resolve the hostname to IP addresses, and find one reachable
address.
+ *
+ * @param hostname the name of the host
+ * @param timeout the time, in millseconds, before {@link
InetAddress#isReachable}
+ * aborts
+ * @return a reachable IP address. If no such IP address can be
found,
+ * just return the first IP address of the hostname.
+ *
+ * @exception UnknownHostException
+ */
+ public InetAddress getReachableAddress(String hostname, int
timeout)
+ throws UnknownHostException {
+ InetAddress[] addresses = InetAddress.getAllByName(hostname);
+ for (InetAddress a : addresses) {
+ try {
+ if (a.isReachable(timeout)) {
--- End diff --
My main problem with this PR is that call to `isReachable(timeout)` for two
reasons:
1) the most important one: `isReachable(timeout)` seems unreliable so there
are plenty cases where it returns false even tough the node is reachable or
vice-versa! https://bugs.openjdk.java.net/browse/JDK-8159410 (google
"InetAddress.isReachable not working" or "InetAddress.isReachable unreliable"
to see further cases).
2) This timeout can add an arbitrary delay until a reachable node can be
tested.
IDK what a good compromise would be for both points above (leaving as it is
today could work, so no problem, even tough I am a bit concerned), but maybe we
could use a solution similar to ZOOKEEPER-2184 and return the next address in
the array (using `next = ++next % addresses.length` to prevent out of bound
exceptions).
> 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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