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https://issues.apache.org/jira/browse/ZOOKEEPER-3100?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16553025#comment-16553025
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Andor Molnar commented on ZOOKEEPER-3100:
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[~rsivaram]
Thanks for testing the new version so quickly and accurately. This is very
useful.
In theory a server should answer on all addresses that it resolves to, so if
the client is unable to connect to the chosen address, host is considered to be
down. That was one the reasons why I was against choosing randomly from the
resolved addresses. The other one is random behaviour is a code smell.
Anyway.
Why is the server not connectable on the IPv6 address? ZooKeeper usually binds
client port (2181) on the wildcard address, which means it listens on all
network interfaces and all protocols. (I'll double check this to make sure.)
What's your server configuration look like?
> ZooKeeper client times out due to random choice of resolved addresses
> ---------------------------------------------------------------------
>
> Key: ZOOKEEPER-3100
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3100
> Project: ZooKeeper
> Issue Type: Bug
> Components: java client
> Affects Versions: 3.4.13
> Reporter: Rajini Sivaram
> Priority: Major
>
> The changes to ZooKeeper clients to re-resolve hosts made under
> ZOOKEEPER-2184 results in delays when only a subset of the addresses that a
> host resolves to are actually reachable. This can result in connection
> timeouts on the client.
> For example, when running tests with a single ZooKeeper server accepting
> connections on 127.0.0.1 on a host that has both IPv4 and IPv6, we have seen
> connection timeouts in tests if client connects using `localhost` rather than
> `127.0.0.1`. ZooKeeper client resolves `localhost` to both the IPv4 and IPv6
> addresses and chooses a random one. If IPv6 was chosen, a fixed one second
> backoff is applied before retry since there is only one hostname specified.
> After backoff, 'localhost' is resolved again and a random address chosen,
> which could also be the unconnectable IPv6 address.
> For the list of host names specified for connection, the clients do
> round-robin without backoffs until connections to all hostnames are
> attempted. Can we also do the same for addresses that each of the hosts
> resolves to, so that backoffs are only applied after connection to each
> address is attempted once and every address is connected to once using
> round-robin rather than random selection? This will avoid delays in cases
> where at least one address can be connected to.
>
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