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From tsuna <tsuna...@gmail.com>
Subject Gracefully changing IP addresses of quorum members?
Date Wed, 11 May 2011 19:53:12 GMT
Hi all,
I have a 5-node quorum with 1 node per rack.  It's unfortunate but it
so happens that I need to free up these 5 racks and move all their
machines somewhere else.  This requires me to change the IP addresses
of all the machines in these 5 racks as they land in other racks.

All our applications are configured with a quorum specification of
"zookeeper".  This ends up being resolved as
zookeeper.datacenter.internaldomain.com, which returns 5 A records.
All our Java applications are also started with
-Dsun.net.inetaddr.ttl=600, just in case that matters, because the JDK
by default has the wonderful idea to cache all DNS names forever
regardless of the TTL.  So with this flag the JDK will cache DNS
entries for 10 minutes maximum.

I reviewed the FAQ (http://wiki.apache.org/hadoop/ZooKeeper/FAQ – BTW
there's a broken image in answer to the 1st question) and the admin
guide (http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html) and
searched on the intertubes a bit, but I couldn't come up with an
answer.

Can I move the ZK machines one by one and re-IP them and hope they'll
rejoin the quorum gracefully?  If I allow like 20-30 minutes between
each machine move, we should always have a quorum, provided that the
machines can re-join the quorum with a different IP.  Is that the
case?  Has anyone tested this?

If that doesn't work, can you think of anything I can do to gracefully
move the quorum?

Thanks.

-- 
Benoit "tsuna" Sigoure
Software Engineer @ www.StumbleUpon.com

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