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From Steve Newman <st...@scalyr.com>
Subject Re: Adding and removing replicas?
Date Thu, 20 Oct 2016 16:26:02 GMT
Thanks for the pointer. This looks like a nice improvement.

If I'm reading http://zookeeper.apache.org/releases.html correctly, this
feature is only available in alpha release. In the near term, I need a
procedure I can follow for a stable release. Is there any documentation
regarding best practices for adding / removing replicas prior to 3.5.0? The
3.5.2 documentation you linked to is somewhat alarming regarding prior

"Prior to the 3.5.0 release, the membership and all other configuration
parameters of Zookeeper were static - loaded during boot and immutable at
runtime. Operators resorted to ''rolling restarts'' - a manually intensive
and error-prone method of changing the configuration *that has caused data
loss and inconsistency in production*."


On Thu, Oct 20, 2016 at 8:03 AM, Rakesh Radhakrishnan <rakeshr@apache.org>

> Hi Steve,
> I'd suggest you to look at ZooKeeper-3.5.2 latest version and use dynamic
> reconfig feature. This will help to resize(add/remove zk server) your
> cluster without restarting entire cluster.
> Please refer the following links to understand more about the dynamic
> reconfig feature:-
> https://zookeeper.apache.org/doc/r3.5.2-alpha/zookeeperReconfig.html
> http://www.slideshare.net/Hadoop_Summit/dynamic-
> reconfiguration-of-zookeeper
> Regards,
> Rakesh
> On Thu, Oct 20, 2016 at 3:19 AM, Steve Newman <steve@scalyr.com> wrote:
>> Apologies for a basic question, but I've been researching and haven't been
>> able to find the answer online.
>> What is the best way to add or remove replicas from a running ZooKeeper
>> cluster, with minimal downtime? To add a replica, the naive answer would
>> seem to be:
>> 1. Prepare the new replica(s), i.e. install ZooKeeper and set up the
>> configuration files.
>> 2. Edit the configuration for all replicas (new and existing) to list the
>> new replicas.
>> 3. Restart all replicas. (Simultaneously? Or gradually, one at a time?)
>> Is this the best way to do it? Step 3 seems scary in a production cluster.
>> Also, will the new replicas smoothly pick up the existing data, or is it
>> better to seed them with a snapshot somehow?
>> Similarly, the naive answer for removing a replica would seem to be:
>> 1. Halt the ZooKeeper process.
>> 2. Edit the configuration for all other replicas to remove the replica
>> that's going away.
>> 3. Restart all remaining replicas (one at a time?).
>> Again, is this the best approach?
>> Thanks,
>> Steve

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