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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 Fri, 23 Mar 2018 11:19:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16411243#comment-16411243
] 

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

Github user anmolnar commented on the issue:

    https://github.com/apache/zookeeper/pull/451
  
    @afine @ijuma I've finished refactoring of StaticHostProvider.
    
    The implementation follows that I explained in my email as **Option-3**:
    
    > - Do not cache IPs, 
    > - Shuffle the names and resolve with getAllByName() every time when next() is called,
    > - Use getAllByName(), but shuffle the list and return the first IP to properly handle
hostnames associated with multiple IPs,
    > - JDK's built-in caching will prevent name servers from being flooded and will do
the re-resolution automatically when cache expires,
    
    The `Resolver` interface which is also introduced in this patch is the solution for the
problem that @afine raised: to properly mock out the `getAllByName()` call in unit tests.


> 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: Andor Molnar
>            Priority: Blocker
>              Labels: easyfix, patch
>             Fix For: 3.5.4, 3.4.13
>
>         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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