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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2184) Zookeeper Client should re-resolve hosts when connection attempts fail
Date Thu, 15 Feb 2018 19:14:02 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16366132#comment-16366132
] 

ASF GitHub Bot commented on ZOOKEEPER-2184:
-------------------------------------------

Github user afine commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/451#discussion_r168578617
  
    --- Diff: src/java/main/org/apache/zookeeper/client/StaticHostProvider.java ---
    @@ -58,48 +61,122 @@
         public StaticHostProvider(Collection<InetSocketAddress> serverAddresses) {
             for (InetSocketAddress address : serverAddresses) {
                 try {
    -                InetAddress ia = address.getAddress();
    -                InetAddress resolvedAddresses[] = InetAddress.getAllByName((ia != null)
? ia.getHostAddress() :
    -                        address.getHostName());
    +                InetAddress resolvedAddresses[] = InetAddress.getAllByName(getHostString(address));
                     for (InetAddress resolvedAddress : resolvedAddresses) {
    -                    // If hostName is null but the address is not, we can tell that
    -                    // the hostName is an literal IP address. Then we can set the host
string as the hostname
    -                    // safely to avoid reverse DNS lookup.
    -                    // As far as i know, the only way to check if the hostName is null
is use toString().
    -                    // Both the two implementations of InetAddress are final class, so
we can trust the return value of
    -                    // the toString() method.
    -                    if (resolvedAddress.toString().startsWith("/")
    -                            && resolvedAddress.getAddress() != null) {
    -                        this.serverAddresses.add(
    -                                new InetSocketAddress(InetAddress.getByAddress(
    -                                        address.getHostName(),
    -                                        resolvedAddress.getAddress()),
    -                                        address.getPort()));
    -                    } else {
    -                        this.serverAddresses.add(new InetSocketAddress(resolvedAddress.getHostAddress(),
address.getPort()));
    -                    }
    +                    this.serverAddresses.add(new InetSocketAddress(resolvedAddress, address.getPort()));
                     }
                 } catch (UnknownHostException e) {
                     LOG.error("Unable to connect to server: {}", address, e);
                 }
             }
    -        
    +
             if (this.serverAddresses.isEmpty()) {
                 throw new IllegalArgumentException(
                         "A HostProvider may not be empty!");
             }
             Collections.shuffle(this.serverAddresses);
         }
     
    +    /**
    +     * Evaluate to a hostname if one is available and otherwise it returns the
    +     * string representation of the IP address.
    +     *
    +     * In Java 7, we have a method getHostString, but earlier versions do not support
it.
    +     * This method is to provide a replacement for InetSocketAddress.getHostString().
    +     *
    +     * @param addr
    +     * @return Hostname string of address parameter
    +     */
    +    private String getHostString(InetSocketAddress addr) {
    +        String hostString = "";
    +
    +        if (addr == null) {
    +            return hostString;
    +        }
    +        if (!addr.isUnresolved()) {
    +            InetAddress ia = addr.getAddress();
    +
    +            // If the string starts with '/', then it has no hostname
    +            // and we want to avoid the reverse lookup, so we return
    +            // the string representation of the address.
    +            if (ia.toString().startsWith("/")) {
    +                hostString = ia.getHostAddress();
    +            } else {
    +                hostString = addr.getHostName();
    +            }
    +        } else {
    +            // According to the Java 6 documentation, if the hostname is
    +            // unresolved, then the string before the colon is the hostname.
    +            String addrString = addr.toString();
    +            hostString = addrString.substring(0, addrString.lastIndexOf(':'));
    +        }
    +
    +        return hostString;
    +    }
    +
         public int size() {
             return serverAddresses.size();
         }
     
    +    // Counts the number of addresses added and removed during
    +    // the last call to next. Used mainly for test purposes.
    +    // See StasticHostProviderTest.
    +    private int nextAdded = 0;
    +    private int nextRemoved = 0;
    +
    +    public int getNextAdded() {
    +        return nextAdded;
    +    }
    +
    +    public int getNextRemoved() {
    +        return nextRemoved;
    +    }
    +
         public InetSocketAddress next(long spinDelay) {
    -        ++currentIndex;
    -        if (currentIndex == serverAddresses.size()) {
    -            currentIndex = 0;
    +        // Handle possible connection error by re-resolving hostname if possible
    +        if (!connectedSinceNext) {
    +            InetSocketAddress curAddr = serverAddresses.get(currentIndex);
    +            String curHostString = getHostString(curAddr);
    +            if (!curHostString.equals(curAddr.getAddress().getHostAddress())) {
    +                LOG.info("Resolving again hostname: {}", getHostString(curAddr));
    +                try {
    +                    int thePort = curAddr.getPort();
    +                    InetAddress resolvedAddresses[] = InetAddress.getAllByName(curHostString);
    +                    nextAdded = 0;
    +                    nextRemoved = 0;
    +                    if (resolvedAddresses.length == 1) {
    +                        serverAddresses.set(currentIndex, new InetSocketAddress(resolvedAddresses[0],
thePort));
    +                        nextAdded = nextRemoved = 1;
    +                        LOG.debug("Newly resolved address: {}", resolvedAddresses[0]);
    +                    } else {
    +                        int i = 0;
    +                        while (i < serverAddresses.size()) {
    +                            if (getHostString(serverAddresses.get(i)).equals(curHostString)
&&
    --- End diff --
    
    Why don't we simplify things and just do this always? In other words, always remove all
serverAddresses that correspond to the curHostString. That way if curHostString goes from
resolving to many addresses to just 1, we remove all of them?


> Zookeeper Client should re-resolve hosts when connection attempts fail
> ----------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2184
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2184
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: java client
>    Affects Versions: 3.4.6, 3.4.7, 3.4.8, 3.4.9, 3.4.10, 3.5.0, 3.5.1, 3.5.2, 3.5.3,
3.4.11
>         Environment: Ubuntu 14.04 host, Docker containers for Zookeeper & Kafka
>            Reporter: Robert P. Thille
>            Assignee: Flavio Junqueira
>            Priority: Blocker
>              Labels: easyfix, patch
>             Fix For: 3.5.4, 3.4.12
>
>         Attachments: ZOOKEEPER-2184.patch
>
>
> Testing in a Docker environment with a single Kafka instance using a single Zookeeper
instance. Restarting the Zookeeper container will cause it to receive a new IP address. Kafka
will never be able to reconnect to Zookeeper and will hang indefinitely. Updating DNS or /etc/hosts
with the new IP address will not help the client to reconnect as the zookeeper/client/StaticHostProvider
resolves the connection string hosts at creation time and never re-resolves.
> A solution would be for the client to notice that connection attempts fail and attempt
to re-resolve the hostnames in the connectString.



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