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From Adam Blank <adam.bl...@gmail.com>
Subject Re: Configuring SolrCloud with Redundancy on Two Physical Frames
Date Wed, 02 May 2018 13:07:53 GMT
Thank you everyone for the useful information.  Would it be easy to
reconfigure an existing clustered deployment to a standalone deployment?
This is what I'm thinking:

I have two physical servers.  I would have one Zk installed on server 1 and
two Zk installed on server 2.  I would have a Solr node on each server,
each with one or more shards.  If server 1 goes down, I should still be
operational.  If server 2 goes down, I would reconfigure the remaining Solr
node and Zk on server 1 as a standalone deployment.  Should that work in
theory?  If so, the only changes that I should need to make would be to
update the zoo.cfg within Zk and to restart Zk and Solr in standalone
mode?

Thanks,
Adam

On Wed, May 2, 2018 at 8:23 AM, Andor Molnar <andor@cloudera.com> wrote:

> Hi Adam,
>
> Zk uses quorum to get agreement between voting servers (leader and
> followers). Quorum is calculated by majority of servers: N / 2 + 1, where N
> is the number of servers. When you only have 2 Zk servers running, the
> quorum equals 2 which means you need to have both servers up and running
> for ZooKeeper to work. In this case you only have a live backup of the data
> basically, but you don't have fault tolerance.
>
> If you would like to have fault tolerance, you need at least a 3rd server
> "physically" separated with approx the same horsepower as the others. If
> you have a weak machine and it's voted for leader, you'll lose write
> performance, if it's voted for follower, you'll lose read performance.
>
> Running 2 physical machines as one, redundant hypervisor might be a good
> option. You can run 3 VMs on top of that and if one of your servers goes
> down, the other one will be able to run all 3 VMs which keeps ZK
> operational.
>
> Hope that helps a little bit on Zk side.
>
> Regards,
> Andor
>
>
>
>
>
>
>
> On Tue, May 1, 2018 at 9:52 PM, Shawn Heisey <apache@elyograg.org> wrote:
>
> > On 5/1/2018 8:55 AM, Adam Blank wrote:
> > > I would like to have a high-availability/redundant installation of
> > > Zookeeper running in my production environment. The problem is that I
> > only
> > > have 2 physical frames available, so that rules out configuring a
> > Zookeeper
> > > cluster/ensemble since I'd only have redundancy if the frame with the
> > > minority of servers goes down. What is the best practice in this
> > situation?
> > > Is it possible to have a separate standalone install running on each
> > frame
> > > connected to the same set of SOLR nodes or to use one server as primary
> > and
> > > one as backup?
> >
> > I'm more familiar with the Solr side of the equation than the ZK side.
> > That said, I do know if you want bulletproof fault tolerance for ZK, you
> > must have at least three separate physical installations.
> >
> > For redundancy of Solr itself in SolrCloud, you only need two hosts, but
> > for ZK, you need three.  The minimal fault tolerant SolrCloud setup
> > would run both Solr and ZK on two servers and a third ZK by itself.
> > That third server would not need much horsepower.  I've heard of people
> > using a laptop or a low-end desktop for the third server.
> >
> > For best results, you would also want redundancy beyond the servers
> > themselves -- power and network for each server ideally would be
> > separate hardware.  Some even go as far as separate racks and/or
> > geographically diverse datacenters.
> >
> > Thanks,
> > Shawn
> >
> >
>

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