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From Shawn Heisey <apa...@elyograg.org>
Subject Re: Spread SolrCloud across two locations
Date Fri, 02 Jun 2017 12:57:29 GMT
On 5/29/2017 8:57 AM, Jan Høydahl wrote:
> And if you start all three in DC1, you have 3+3 voting, what would
> then happen? Any chance of state corruption?
>
> I believe that my solution isolates manual change to two ZK nodes in
> DC2, while your requires config change to 1 in DC2 and manual
> start/stop of 1 in DC1.

I took the scenario to the zookeeper user list.  Here's the thread:

http://zookeeper-user.578899.n2.nabble.com/Yet-another-quot-two-datacenter-quot-discussion-td7583106.html

I'm not completely clear on what they're saying, but here's what I think
it means:  Dealing with a loss of dc1 by reconfiguring ZK servers in DC2
might work, or it might crash and burn once connectivity to DC1 is restored.

> Well, that’s not up to me to decide, it’s the customer environment
> that sets the constraints, they currently have 2 independent geo
> locations. And Solr is just a dependency of some other app they need
> to install, so doubt that they are very happy to start adding racks or
> independent power/network for this alone. Of course, if they already
> have such redundancy within one of the DCs, placing a 3rd ZK there is
> an ideal solution with probably good enough HA. If not, I’m looking
> for the 2nd best low-friction approach with software-only.

Even if all goes well with scripted reconfiguration of DC2, I don't
think I'd want to try and automate it, because of the chance for a brief
outage to trigger it.  Without automation, if the failure happened at
just the wrong moment, it could be a while before anyone notices, and it
might be hours after it gets noticed before relevant personnel are in a
position to run the reconfiguration script on DC2, during which you'd
have a read-only SolrCloud.

Frequently search is such a critical part of of a web applications that
if it doesn't work, there IS no web application.  That certainly
describes the systems that use the Solr installations that I manage. 
For that kind of application, damage to reputation caused by a couple of
hours where the website doesn't get any updates might be MUCH more
expensive than the monthly cost for a virtual private server from a
hosting company.

Thanks,
Shawn


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